By Jin-yeong Yi
“It may be remarked incidentally that the contentions of philosophers are often much more justifiable when they are arguing against other philosophers than when they pass on to expound their own views, and as each one generally sees fairly clearly the defects of the others, they more or less destroy each other mutually.”
—René Guénon, The Reign of Quantity & the Signs of the Times
“Philosophy consists very largely of one philosopher arguing that all others are jackasses. He usually proves it, and I should add that he also usually proves that he is one himself.”
—H. L. Mencken
“I cannot refute you, Socrates, said Agathon: Let us assume that what you say is true.
“Say rather, beloved Agathon, that you cannot refute the truth; for Socrates is easily refuted.”
When it comes to determining truth, it seems that most people today are overly obsessed with the Who, rather than the What. They tend to scrutinize the conveyor of an idea more than the idea itself. This would explain the ubiquity of argumentum ad hominem, because according to the logic of such people, if you destroy the credibility of a person, you effectively destroy their arguments as well. Thus people who are eager to, say, refute Nietzsche spend more time focusing on his psychological condition than his philosophy; they glibly assume that his insanity in his final years proves that he was wrong all along, forgetting (or simply not realizing) that ideas are to be evaluated independently, and that truth is truth, no matter where it is found (hint: the statement 10 x 10 = 100 is true, even if it’s uttered by a schizophrenic). Ideas stand or fall on their own.
For related reasons, I recognize that appeals to authority are ultimately futile. Consider this observation by Sextus Empiricus:
“[L]et it be granted and established that objects ought to be judged by Man. Then, since there exists great difference amongst men, let the dogmatists first agree together that this is the particular man to whom we must attend, and then, and only then, let them bid us also to yield him our assent. But if they are going to dispute about this ‘long as the waters flow on and and the tall trees cease not to burgeon’ (to quote the familiar saying), how can they urge us to assent rashly to anyone? For if they declare that we must believe the sage, we shall ask them ‘What sage?’”
You can hide behind your Nietzsche, your Dostoevsky, your Gödel, your Popper, your Wittgenstein, your Dennett, your Hawking, or whomever you read, and have them argue your case for you by quoting them at length, but if you consider yourself a “real” freethinker (or at least an aspiring one, if true freethought is impossible), you will ultimately have to draw your own conclusions on the issues at hand, as daunting a task as that may be. At the end of the day, arguing from authority is self-defeating, as even that requires you to make your own judgment, namely, judgment on who wields the greatest authority on which issue.
 See Outlines of Pyrrhonism by Sextus Empiricus.