Shamefully, until the last week or so, despite possessing two degrees partly in philosophy, I have never read a philosopher earlier than Hobbes. The Greeks, Thomism, disputes over nominalism, it all passed me by - unless MacIntyre talked about it in 'After Virtue' or 'A Short History of Ethics', in which case I might be able to summarise roughly what he thinks about it, which is probably not much use at all. Now, though, since I need to be able to teach it, I am reading Plato's Republic. Now, obviously, Plato is a hectoring, life-denying, totalitarian, conservative loon, or at least he is in The Republic, and so reading him is very tedious. However, it does make a whole load of other stuff that goes on in political theory make more sense: if you think of much of philosophy as debating questions which Plato asked, then of course hammering home the thought that what Plato said is hectoring, life-denying, totalitarian, conservative, and loony, is going to be important. Indeed, anything which looks even remotely like Plato is going to bring back visions of a utopia apparently as imagined by someone whose intellectual diet consisted solely of the headlines of Daily Mail editorials - banning all forms of story-telling in which anything other than the neutral recounting of narrative occurs, since it's lying, for f*ck's sake - and so provoke repulsion in much the same way. Thus, the thought that philosophy involves disengagement from the world; the thought, particularly current in [cue generalised handwaving] more Continental circles, that saying there are answers of some sort is a kind of authoritarianism; the thought, current in the same kind of circles, that saying that there are answers of some sort involves crazy metaphysics; and probably a whole load of other things that I can't think of off the top of my head. I once prompted the description of Richard Rorty as being tedious partly because he was constantly kicking at Plato's shins: once you've read him, kicking is clearly insufficient.
Addendum, 06/01/08: Obviously, to understand is not to justify. It may not even really be to understand. For example, even if you hated Plato, and justly so, it's not entirely clear why you'd write Vol. 1 of 'The Open Society And Its Enemies'. For one thing, the effacement of various subtleties involved in the analogy of city and soul in a shitstorm of accusations of collectivism and the associated granting of moral personality to the state is just so obviously wrong that it's totally counterproductive. Plato thought that it was best for the mass of the people to be ruled by the guardians; that's the point of all the 'to each according to their nature' stuff. What's offensive about that isn't that the state acquires moral standing separately from its citizens, because that doesn't give moral standing to the state separately from its citizens, it's that someone else gets to impose this really, really crazily reactionary idea of your nature on you for own good.