We disagree on the particulars of what we might call "principled", and I don't think I'm "misunderstanding" human nature (what does that mean, anyhow?) But yes, I am stretching the rubber band a bit far when I include "principled" suicides in presumably "non-principled" cases where that might presumably not be the case, as for instance in the lives of certain poets, perhaps, who have taken their lives for reasons not inherently principled, but merely assumed. If Hölderlin had committed suicide, a man who was "benighted" by insanity yet a poet of the deepest feeling, I would not consider that "principled", even though his biographers or admirers might have considered it such.
Which brings me to my point that I don't believe "conviction" to be appropriate in applying to most cases (I wager it's something else, not "desperation" but something a bit more ambiguous in nature), and that there's a certain airiness with which I apply the label to "noble causes." You're correct, perhaps they believe themselves to have conviction at heart, though as someone working outside of their mind I can only conceive of their judgement as "exhausted" by particular circumstances. "What we term virtue is often but a mass of various actions and divers interests, which fortune, or our own industry, manage to arrange; and it is not always from valour or from chastity that men are brave, and women chaste." When people consider suicide an inviolable wrong, it's one side of the same coin.
I do not think that is the case. The reasons for suicide are in abundance. What I call "mental sclerosis" or "insurmountable anguish", you would deem a rational diagnosis, a thing born out of absolute "rational choice", which I don't agree with. I'm using the term "rationality" loosely, but basically most suicides are only "purpose-based" in the sense of trying to cessate life. Mishima's suicide was not just "self-destructive", but rebirth, or "immortalization", though that's assuming he didn't want to die, but was ready to die. A soldier. A soldier, however, who accepts death is not "principled" but merely realistic, whereas Mishima was a soldier involved in a time purged of warhorse heroism, a time earmarked by the revolution of the "individual."
Your suicide may well be "principled", I don't know you and never will, perhaps you are an exception. It isn't my call. I know my suicide won't be "principled", so perhaps we are both projecting some mental state onto a "real" state-of-affairs, and my view could be just as specious, or more. I can't say. I could also consider my suicide as "antagonistic" of the world, a "quiet protest", though that's just my own particular neurosis, it might be lost or misconstrued or forgotten after a time.
I haven't read C&P since I was around twenty-something... Raskolnikov's ending always struck me, the Napoleonic spirit with which he carried himself may have been brought about by particulars (as most would perceive him as a "madman" from the outside), but his redemption is unequivocally "principled" in a sense that I could never be, for to me it is far harder (not noble, but "harder"), to live in a world which is antagonistic to you. In both cases where one might die for an ideal and the other might live for one, the former is subject to the pettiness of man, while the latter is "lived, cherished", hence why in my earlier post I said that the self-destruction of the moral agent is an irony of cosmic proportions. I don't mean that as condemnation (look where I am). I just don't see the act of suicide as something whose value ought to be bottled up in the way that deeds or vices are.
Sorry for longpoast.