What tempts us to look at all philosophers half suspiciously and half mockingly is not so much that we recognize again and again how innocent they are, how often and how easily they make mistakes and lose their way, in short their childishness and childlike-ness -- but rather that they are not sufficiently candid, though they make a great virtuous noisy to-do as soon as the problem of truthfulness is even remotely touched upon. Every one of them pretends that he has discovered his opinions through the self-development of cold, pure, divinely untroubled dialectic (in distinction to the mystics of every rank who, more honest and fatuous, talk about "inspiration"), whereas, at bottom, a pre-conceived dogma, a notion, an "institution," or mostly a heart's desire, made abstract and refined, is defended by them with arguments sought after the fact.
It is in some ways an ad hominem attack - but it's true. And the actual argument, that philosophers defend arguments "sought after the fact", is not an ad hominem attack. It may be more similar to a genetic fallacy.
Gradually I have come to realize what every great philosophy up to now has been: the personal confession of its originator...