Why I cannot consent to be killed?

Question

My friend and I had an argument about the subject. He argued that in some circumstances it should be legal to consent to be killed (e.g. if the dominant kills the submissive during the BDSM session and both are OK with that).

I found that idea rather stupid because, in my opinion, it would make society less safe to live in. But I wasn't able to win the argument, because I didn't have enough information about the topic, that's why I am trying to figure out it now.

As far as I understood, in most countries (probably all of them, but I am not sure) it is illegal to kill a person no matter if they consent to it or not. What I want to understand is why they can't consent. What is the reasoning for lawmakers to design the law this way and not another?

I tried to Google the question, but for the most part, sources just state the fact that it's illegal, and not why it is illegal. And the ones that do explain the reasoning explain it in the context of euthanasia, and it's not what I particularly care about (in the context of this question of course).

(The question was originally asked on law.se but people there became unhappy with it and told me to ask it here instead)

Answer 1

German cannibal Armin Meiwes apparently got enthusiastic consent from his victim, to start eating him as he watched. That is perhaps a more clear case than BDSM practices. And it certainly challenges an entirely consent-based picture of sexual relations.

Suicide used to be illegal in Christian countries, despite a persons 'consent'. That used to be responded to by not being buried on holy ground. In terms of the courts, these laws tended only to relate to suicide pacts where one person survives, and they could be held responsible for the other persons death.

From Wikipedia.

Jurisdictions as you can see have varying views on whether you can consent to your own death. So trying to arrive at one universal answer for all places is clearly only for philosophy, not law.

You can consider consenting to death by BDSM as a form of assisted suicide, and the Meiwes case clearly shows some people develop fixations that relate to them wanting death involving specific circumstances. In the relatively few places that allow assisted suicide, substantial safeguards are put in place to screen for untreated mental health condition, and coercion by others, and so on. Canada has allowed a case of assisted suicide for mental rather than physical health reasons. See BBC article Who can die? Canada wrestles with euthanasia for the mentally ill. I would say it's possible to imagine a future where certain kinds of BDSM suicide were made legal and safeguards were in place to prevent wider dangees, although it's hard to imagine it becoming a legislative priority.

An interesting point is that we can consent to a very serious risk of death, in war. But, I would argue that no one can be ordered to certain death, it can only be volunteered for, because no enforcement more severe than death can be used to coerce someone. Discussed here: Exploring philosophy behind "Catch-22" novel: individual in war

Answer 2

So, IANAL, but the tradeoffs that come to mind here are simplicity and precedent. Namely (numbered for reference, not relative importance):

1. It's much easier to decide whether exceptions apply if the answer is always "no, they don't".
2. One explicit exception will invite people to suggest other exceptions that they believe should be made explicit. Not everyone will agree, especially on a topic like killing, and those disagreements risk polarizing people into mutually hostile groups. See, for example, debates over abortion in the United States (which also, according to at least one side of the debate, involves killing).
3. Consent is fuzzier than it sounds, per Futilitarian's comment; but, more importantly for murder, it is much harder to confirm after death. Absent a police officer (or judge, or...) in the room at time of ostensibly-consented-to death, most methods of determining that consent can be faked (to varying degrees of plausibility).
4. A would-be criminal who plans things beforehand can look up the law in question and plan their crime to look like one of the exceptions. This is particularly harmful for murder for the obvious reason, and also because - if successful - it inherently removes the most immediate witness.
5. People who have murdered one person are an order of magnitude more likely than the general population to murder someone (else). Disentangling this effect for any specific exception will be very tricky to pull off morally.
6. There are already exceptions for accidental death or risky activities (e.g., skydiving, rock climbing), at least in most US jurisdictions, and probably where you live too - risk is everywhere, after all. Why are the approaches there insufficient?
7. Related to (3) and (4), legally accepting consent to be killed benefits honestly suicidal people, but at the expense of people who end up killed by murderers who think they're clever enough to escape via the new loophole (regardless of whether they actually are).
8. As an empirical test case, Canada did pass an example similar to what you describe a couple of years ago, albeit for medical situations rather than sexual ones. There have definitely been concerns, despite the safeguards introduced before implementation.