When you say "Would it be good if everyone was good?"
you imply, as far as I can tell, two different types of good. I think the first definition of good you are talking about is good vs bad. Which is more of a positive vs negative way of looking at it. With the second "good", I think you mean that people cannot inflict evil, meaning, doing good (pleasing, helping, loving, caring) is all thats left within a human.
Im also assuming that with "everyone is good"
you mean that they are good forever and always have been, instead of just at a specific time in history. In that case it would mean that evil does not exist (or atleast is never used by people). Moral evil, to be specific (I think moral evil is the only evil that exists, see here why). In this case it is simply true that this is a "good" (morally) world. People do each other no harm and live peacefully together. Tragedy still exists though, so people still suffer.
Looking at human biology (which id say is mostly still the same) we probably will have way more trouble handling suffering. When you are born, your upbringing has the most impact on your mental state. If you never experience evil pain from birth up untill, for example, your thirties, you will probably go into depression very quickly once a relative dies or an lightning bolt hits your friend. Tragedy would be felt more painfull than ever before. You can see this as a negative result of everyone being good (morally). In this idea, it is indeed "good" (positive) that sometimes people are evil (morally). They prepare you from bigger difficulties in life. Very paradoxical.
Just to be clear:
- If everyone is good (morally), then no evil exists.
- If everyone is good (morally), then humans can still perceive evil when someone brings it up as an idea. The definition of moral evil, Moral evil is any morally negative event caused by the intentional action or inaction of an agent, such as a person, can still exist if we all act morally good. People just have to bring up this idea for it to be perceived.
- If everyone is good (morally), then appreciating one's personality is the only thing humans can do. Hating one's personality or disliking it, by expression, is evil. Which is impossible in a morally good world.