Consent requires someone to be of sound mind though. Someone can’t consent to sex when they’re drunk. I would argue that there are some activities where simply consenting to them is demonstration of mental malady or incapacity. A rational and mentally well person would not consent to have themselves voluntarily killed by a serial killer. If you post an ad offering to let someone literally tear you to pieces, you’re clearly not of sound mind. Now, I’m not in favor of punishing people for surviving an attempted suicide, but I am perfectly fine punishing people who would take advantage of mentally unwell suicidal people by getting them to consent to all sorts of horrible and lethal things.

It’s different in the case of medically assisted suicide that the person is not irrational. Someone of perfectly sound and rational mind can recognize that a slow, painful, and humiliating death is worse than a quick and painless one. If religion weren’t a factor, most people with diagnosis like Alzheimers or painful untreatable cancers would end up going that route.