I saw that most others figured not everyone would be. But I pretty much figure everyone would be capable, and not only would be capable of it, but would ask/beg for the chance for it. I'm not saying what they'd have to be put through isn't absolutely cruel to the point of horror movie writers being like "whoa, that's too much", and not saying things involved wouldn't have been targeted just for that goal for some. But eventually I think everyone would be broken to that point.
I figure most here are going with normal life events, I'm opting for a psychotic person going around with the goal of driving people to it at all costs, and nothing being off limits.
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Even that aside, I think most people would opt for it if they weren't told it was wrong, eternal damnation would await them, uncertainty in the afterlife, etc. Seriously, if you include DNR's into it (which is basically 'you can be saved without problem, but let me die' even if healthy shy of who knows what that could be a simple chemical spill at work, or a heart issue), or even stopping say chemo, or dialysis (which the latter will kill you)--all which in a sense is a death that you know can happen, sometimes you know when...or even a "don't keep me alive if I'm a vegetable" like thing.... include those? we're probably talking almost everyone right there.
It's just varying degrees to what people consider "suicide" and what's acceptable to them for living. Think of it.... let's say person A discovers they need dialysis, but ctb's, person B is on dialysis, but decides to end it causing their death. Why is one considered good, and the other bad? They both died because of dislysis, both by their own hand, just one took action, one took inaction. (I've wondered this because of my grandparents actually--one nwanted to ctb, family stopped because was one, one stopped dialysis "omg that's so brave!" like)
Anyway, short answer: I believe anyone is capable, some just might have wished they had over the alternative.