For me I think if an adult wants to die then let them. Until we gain the technology to body jump and can literally walk a mile in someones shoes we have no way of knowing what they are truly going through and thus it is not any of our business.
Though for me I wouldn't even say I am against suicide of someone who isn't sick. Let me explain: I don't encourage this and obviously it is a mental illness, but if someone takes depression meds and shit and it still doesn't help and they want to off themselves? Then as long as they do it in a way that doesn't harm others I say..meh, because other we'd just have to keep them locked up under suicide watch, and probably even doped up. Which is no way to exist.