I have only one thing to add to the last post, on Schopenhauer, concerning his personal behaviour. Wikipedia cites Betrand Russell's complaint that Schopenhauer did not at all live the life of asceticism that he extolled. Schopenahuer himself provided an anticipatory response, also cited in the article, "In general, it is a strange demand on a moralist that he should commend no other virtue than that which he himself possesses. To repeat abstractly, universally, and distinctly in concepts the whole inner nature of the world, and thus to deposit it as a reflected image in permanent concepts always ready for the faculty of reason, this and nothing else is philosophy."
While it is true that a person's philosophy does not depend ultimately on whether he himself follows what he teaches, it is nevertheless a relevant matter to consider. If a person were to proclaim publicly that there can be no earthly happiness outside of complete chastity, and yet spend his evenings chatting up ladies at the bar and engaging in one-night stands, one would have cause to doubt the truth of his statements -- or at least whether he sincerely believed them. To cite a somewhat later 19th century philosophy, Pragmatism, "belief is that on which one is prepared to act" (citing Wikipedia, again). It is not necessary that a person who believes abstinence to be a virtue also be a great abstainer, but one would at least expect such a person to desire to abstain more, to attain more closely to his ideal. Christians are notoriously bad at living up to their moral goals, but their whole religion presupposes their failure and expects them to try, fail, and ask forgiveness of God. If Schopenhauer showed no interest in renouncing his own will, even as he proclaimed that happiness is only to be obtained in that fashion, then there is reason to be sceptical whether he really believed it. (I have done no research into Schopenhauer's personal life, and therefore I leave it an open question whether he did or did not attempt to practice his own philosophy. However, I think his defense quoted in the opening paragraph is extraordinarily shallow and unconvincing. I would also add that his being a complete hyprocrite would not prove that his philosophy was wrong; however, considering what exceptional demands of renunciation it puts on individuals, and the ecstasy it promises to ascetics, I would certainly be inclined to doubt its truth if he himself had no interest in practicing what he preached.)
** (A week later:) I wanted to add a clarification that the situation would be quite different if Schopenhauer had said that self-denial was the morally correct thing to do, but acknowledged that it would be painful. Anyone may be forgiven for failing to live up to standards that he acknowledges to require foregoing pleasure. According to Schopenhauer, however, anyone who can see past the veil of illusion (maya) can see that all willing is self-defeating and ultimately painful. Since he writes about it, presumably Schopenhauer himself is capable of seeing past the veil of illusion, at least sometimes, so what advantage can he gain by perpetuating a situation that he sees to be self-defeating?