So yes: why study those who have been proven wrong? And I mean this not in an overarching, “why this?, why that?” sort of asking, but in the strong practical sense: why spend time reading (understanding, taking notes, remembering etc.) those whose ideas are in your present climate… obsolete. In fact, if we dig deeper into this question, I think we might rephrase it as: Why study philosophies which have been, in one way or another, rendered useless by other, more recent philosophies? In this format, one might see the question as only applying to ancient (or at least pre-modern) philosophies and theories – and to the study of those philosophies en tant que philosophies. [I’m using the words “philosophy” and “theory” carelessly]. Of course we could look at the writings of Aristotle from any number of views: we could check their grammar, lexicon, or literary merits. But en tant que philosophies, how can the Nicomachean Ethics apply to us, the YouTube & iPad generation?
The question, nonetheless, applies to any (and I think it’s possible here to speak of ANY-any) idea which is, in some way, out of date. Think of logical positivism. Among all the noisy, for the most part ideologically-driven ideas, some are good, some are bad. But qua philosophy, logical positivism has long been thwarted even by some of its main admirers. In this case, aside from the more profitable byproducts, why bother?
The answer that “you have to understand the supporter to understand the contender” is, again practically speaking, somewhat old-fashioned. With encyclopedias, internet, and fast-search websites popping everywhere, it might be gratifying, but it’s hardly necessary to read Out of Date Scholar X, cover to cover, in order to fully understand and appreciate Up to Date Detractor Y of Out of Date Scholar X. There is a risk of unfair straw men getting heavier and heavier by such practices – but I’d say that most of the time, the bluffs are called and writers know that. Access to sources, constantly improving since the invention of printing, works to prevent (or at least unveil in the aftermath) blatant dishonesties.
Speaking about Heraclitus, Bertrand Russell involuntarily gives his personal answer to our question. The passage might also be read as the motivation for undertaking the gigantic project of writing a history of philosophy. Biased by my interests as I might be, I find much sense in the idea that from an argumentative point of view, any sane, consistent set of arguments that compile (or not) into a philosophy, is a “readable” intellectual product.
In studying a philosopher, the right attitude is neither reverence nor contempt, but first a kind of hypothetical sympathy, until it is possible to know what it feels like to believe in his theories, and only then a revival of the critical attitude, which should resemble, as far as possible, the state of mind of a person abandoning opinions which he has hitherto held. Contempt interferes with the first part of this process, and reverence with the second. Two things are to be remembered: that a man whose opinions and theories are worth studying may be presumed to have had some intelligence, but that no man is likely to have arrived at complete and final truth on any subject whatever. When an intelligent man expresses a view which seems to us obviously absurd, we should not attempt to prove that it is somehow true, but we should try to understand how it ever came to seem true. This exercise of historical and psychological imagination at once enlarges the scope of our thinking, and helps us to realize how foolish many of our own cherished prejudices will seem to an age which has a different temper of mind. (Russell, 1946, p. 39)
Not to mention the ever-threatening risk that Out of Date Scholar X was right after all.