Reducing Suffering: Arguably the most common motivation of antinatalists is the fact that one creates suffering by having a child. If you reproduce, you can be certain that your child will experience suffering. Illness, sadness, existential dread and injuries are the most obvious consequences. Other forms of suffering, like bullying, rape, violent crime, abuse and discrimination, are not guaranteed, but they are not improbable. Sometimes suffering manifests itself in ways that are so ordinary that you might not even think of them straight away. However, we all constantly experience suffering in the form of hunger, thirst, desire to void, work, physical exertion, tiredness, frustration, disappointment and many more. All of those are inconveniences without which life would be far more comfortable. Work for example even takes up a significant amount of our time. Who he has a child usually condemns it to decades of work.
One might argue now that some sufferings like hunger and tiredness are balanced out by delights like eating and sleeping. On the one hand, though, such an argument is only true for those who enjoy eating and sleeping, on the other hand, and more importantly, such delights only appear as positives as they release us from a suffering. And while a suffering like hunger gets painful after some time and can eventually kill you, its release through eating only lasts shortly. After a few hours, hunger appears anew. We as humans are permanently obedient to our basic urges and needs. If we do not relieve sufferings like hunger by eating regularly, our body downright tortures us to death. You do not to express it so drastically, but on closer consideration, our lives turn out to be an endless attempt to reduce major and minor suffering.
The argument of reduction of suffering is still weighty if you do not count states like hunger as suffering. Even if you ignore major harms like severe injuries and diseases that befall a lot of us. Take into consideration the following: Every procreative human knows that terrible atrocities like rape and torture could happen to anybody at any given time. The risk might be low in some cases, but every person who procreates takes the risk of it happening to his child. They gamble in a way – the stake being the life of a person that has no say in that situation.
Veganism: A newborn will probably consume animal products in his lifetime. A vegan who has a child consciously takes the risk that animals will suffer as a consequence of their actions. Whoever truly cares about animals should reconsider having children. (Note: not every antinatalist is automatically a vegan.)
Environmentalism: Some people take the view that humans damage the planet and thus refrain from having children. In my experience, they constitute a minority among antinatalists.
Adoption: Why should you have a child of your own when there are so many orphans in the world? There is not really anything to add to this reason. I should remark here that antinatalists do not oppose adoption. They can very well have children that way and often see providing an orphan with a new home as a noble deed. If you decide to invest your resources in raising a biological child instead of helping an already existing one, you just create more life capable of suffering instead of helping somebody in need.
Religion: Religion could lead to antinatalism for various reasons. Personally, I have never personally met a person with such a motivation , so I can not say with certainty in what way it might actually occur.
Classical Buddhism expresses several antinatalist ideas. The thought that life is suffering is already thousands of years old. Religious views underlie personal interpretation of course. That Buddhists aim to attain nirvana (interpreted by many as “non-existence”) by preventing their rebirth could possibly bring somebody to antinatalism. The principles of suffering reduction and overcoming bodily urges and constraints are stated as well.
Those who believe in some sort of hell and do not want to inflict suffering should not procreate either. If you are convinced that your own child might end up in hell, or is even born a sinner, and still subject them to that risk, your moral principles are questionable.
Consent: The fact that life contains suffering might be tolerable under certain circumstances, i.e. if one could choose they want to live such a life. Actually, we are all here without our consent. Our parents condemned us to suffering and death because of their own, personal wishes; no one can deny that. (Forced marriage and pregnancy in some regions of the world is the obvious exception. Still, it is people other than the parents who are responsible in that case.) Consent is an important moral principle, though. It is the reason why it is illegal to sexually abuse a drunk person, or to produce child and animal pornography.
One might now argue that most people do not complain about their birth in hindsight. Apart from the fact that they might do complain if procreation were not taken for granted by society, the argument does not hold moral value. When you approach a stranger in the streets, break their arm and then gift them a suitcase full of cash, they can justly sue you on grounds of battery. You can not argue that you wanted to benefit them on the whole. You have simply inflicted suffering on somebody without their agreement.
A lot of people counter the consent argument by saying that the unhappy could simply kill themselves. While that is true, it is problematic for several reasons. In order to entertain the idea of committing suicide, most people have to have experienced a substantial amount of suffering. On top of that, suicide is difficult to realize as it requires you to overcome your survival instinct, which takes much strength. Even if you achieve this, it is not easy to overcome your body. Jumping off a tall building, for example, requires additional courage, moreover such a method can end up traumatizing or injuring other people. Further, no method is really safe: Jumping off high buildings or bridges, shooting, poisoning, hanging, self-immolation, electrocution etc. are methods that can be survived. They all include the risk of ending up severely disabled in the worst case, resulting not in salvation but in a harder life.
Suicide is a social taboo – which also makes it more difficult. Were it seen purely as an alternative to living, and physicians performed assisted suicide, it would already help a lot. Instead, you have to keep your suicide plans a secret and rely on delicate methods. You are not granted the option to say farewell to friends and the like and usually die alone. A lot of people do not commit suicide because they do not want to force anybody to put with disposing of their remains once they are found. If suicide were accepted in society, you could die with medical assistance, pain-free and among familiar faces. You could easily donate your organs and therefore even help others.
Hedonism: Even though it does not count as antinatalism, which describes a philosophical position, I want to mention the “Childfree” movement. Its adherents decide not to make and raise children for personal reasons. They often justify that in view of their dislike of children or the financial and time-wise burden a child places on their parents. As they are not philosophically motivated and also oppose adoption more often than not, they are not antinatalists. Notwithstanding, they are an important community as women in certain parts of the world (and less frequently men) are urged into procreating by their surroundings for social or religious reasons. In extreme cases, they are accused of egoism, unmanliness or immaturity if they remain childless. The Childfree movement opposes such societal constraints and makes people question child-rearing in general.
Overpopulation: This is not necessarily about antinatalism either. The fact that overpopulation and climate change may get problematic should be clear to everyone. Even many pro-natalists are aware that at least controlled population growth or controlled population reduction might be necessary in order to avoid a catastrophe. Pondering on population issues can make someone an antinatalist.
Benatar's Asymmetry: Philosopher David Benatar presents in his book “Better Never to Have Been” an asymmetry that exists between existence and non-existence. I can not outline his whole work on here; reading his book is heavily recommended. Put simply, the asymmetry illustrates how not existing is preferable over existing in any case. When you exist, you experience positive things, which is good, and negative things, which is bad. When you do not exist, you do not experience negative things, which is good. You also do not experience positive things, which is not bad, though, as not experiencing good things is only perceived as suffering when it is deprivation. Thus, non-existence is preferable as you do not experience suffering and are also not able to miss the delights you miss out on. To put it in a rather humorous way as an analogy: Have you ever felt pity for the poor non-existent inhabitants of Ernst Thälmann Island, for they can not behold the beautiful Caribbean beaches?
Russian Roulette: Now, I want to offer an analogy that everybody should take to heart: When somebody reflects upon having a child, he would accept the risk of his child experiencing affliction, a congenital disorder for example. If he goes on to create a child, he decides to gamble. He plays a game of Russian Roulette, only that he does not point the gun at his own but at the head of another person that did not agree to take part.
Let us suppose you conceive a child that has a severe disability and the child asks you why you went ahead and procreated if you knew about disabilities. What would your answer be? That nobody ever expects to be affected by such grave things themselves? I do not think a satisfying answer could be found.
Politics: If you are unhappy with the politics of your country or the world, you should reconsider whether it is acceptable to force children into this system. Even in wealthy countries, huge inequality exists and the majority of people depends on working in a capitalist system (that some call exploitative) just to fight for a right to exist. If you have a child, you force them to work and risk that they get poor at some point down the line. On top of that, you support the current system by feeding it another person.
Precisely speaking, people are already subject to massive coercion during their childhood. They are forced to attend school and are under parental authority right from the start.
Egoism of Having Children: Birth usually results from a wish of the parents. The parents never act in the child's interest – having children is always an egoistic action. The reasons for it vary: You want to prove your maturity or manliness, you find babies cute, you need a worker for the family business, you want your family tree to grow bigger, you want to create workforce or soldiers for your nation, you want to outnumber other states or religions, you dream of a storybook family, you want to bind your partner to you, you crave appreciation, you want to realize your squashed your childhood dreams vicariously through your child, and so on.
The point is that procreating is always a egoistic decision. No non-existent child is begging you out of nirvana to finally introduce them to the world.
Pointlessness of Life: For all we as humans know, we can only assume that life is pointless. We are born onto a piece of rock dashing through space as part of a process of chemical reactions, only to die some years later and suffer and crumble into dust in the end. Pointlessness is seen by some as something positive, but having a human suffer needlessly by giving birth to them is questionable. That pointlessness only further strengthens the case for the suffering and the consent arguments.
Since I like quotes:
“If children were brought into the world by an act of pure reason alone, would the human race continue to exist? Would not a man rather have so much sympathy with the coming generation as to spare it the burden of existence, or at any rate not take it upon himself to impose that burden upon it in cold blood?” - Arthur Schopenhauer
“It is curious that while good people go to great lengths to spare their children from suffering, few of them seem to notice that the one (and only) guaranteed way to prevent all the suffering of their children is not to bring those children into existence in the first place.” - David Benatar
“A coin is examined, and only after careful deliberation, given to a beggar, whereas a child is flung out into the cosmic brutality without hesitation.” - Peter Wessel Zapffe
“Things change in an instant. Two things, however, are certain. Everyone will suffer. And everyone will die.” - Jim Crawford
“I was alone in that cemetery overlooking the village when a pregnant woman came in. I left at once, in order not to look at this corpse-bearer at close range, nor to ruminate upon the contrast between an aggressive womb and the time-worn tombs-between a false promise and the end of all promises.” - Emil Cioran
“If destruction is violence, creation, too, is violence. Procreation, therefore, involves violence. The creation of what is bound to perish certainly involves violence.” - Mahatma Ghandi
“Despite the fact that neither anti- nor pronatalists can prove their positions, pro-natalists have to live with the possibility that they might be wrong. That is a heavy burden to carry, and a heavier burden to pass on to subsequent generations. Antinatalists don’t have a similar burden. When action is taken on their side and a child is not born, no harm is done. No one has to suffer and die.” - Thomas Ligotti
“The idea of bringing someone into the world fills me with horror. I would curse myself if I were a father. A son of mine! Oh no, no, no! May my entire flesh perish and may I transmit to no one the aggravations and the disgrace of existence.” - Gustave Flaubert
“Never to have been born is best but if we must see the light, the next best is quickly returning whence we came. When youth departs, with all its follies, who does not stagger under evils? Who escapes them?” - Sophocles
“Every existing thing is born without reason, prolongs itself out of weakness, and dies by chance.” - Jean-Paul Sartre
“When we are born, we cry that we are come to this great stage of fools.” - Shakespeare, King Lear
“Why is it that we rejoice at a birth and grieve at a funeral? It is because we are not the person involved.” - Mark Twain