Fundamentally Post is wrong and everyone else linked to above is right: Jefferson was worse on slavery and worse on race that his contemporaries (in both the United States and France, a rare case in which he accorded no apparent weight to the views of his friends in the salons). Moreover, I think it is clear that he knew slavery to be wrong, at least early in his life; there’s no anachronism in our judging him on the basis of moral knowledge that was available to him. It’s surely absurd to say, as Post does, that Jefferson made crucial contributions to the end of slavery, no matter how much use abolitionists and Lincoln were able to make of the words of the Declaration.
I agree in particular with Cowen that Jefferson was not the wisest of political thinkers among the founders. He had a broad but shallow brilliance, and in his disagreements with either Madison or Adams he always comes across as more clever than insightful. He comes out somewhat better in the great debate with Hamilton, but not sufficiently so. Like Franklin, he left an institutional legacy outside the main institutions of constitutional government, but made no great innovations or discoveries within those institutions.
But I don’t much like the framing of Jefferson as a “monster.” It’s too distancing. Jefferson’s contradictions are central to American political life; white Americans in particular should view his contradictions as our own. It’s true that he enunciated principles of liberty that had enduring moral power; it’s also true that he committed great evil as a slaveowner. In his attempts to rationalize the contradiction he lent his legitimacy to, indeed helped to formulate, a new, ugly brand of “scientific” racism that was to badly infect the American psyche. Aristocratic monarchies, societies based on class distinctions, had no need for racist ideologies to justify their hierarchies; a society ostensibly founded on a doctrine of equality did. Montesquieu and Smith both understood the dynamic, and maintained that slavery would be particularly hard to eradicate in democratic republics; and so it was. Herrenvolk democracy is both egalitarian within the master race and viciously inegalitarian as between races, and one doesn’t understand the phenomenon if one insists that one side of that coin is more real than the other. White America was freer and more equal than contemporaneous European societies; America was a slave state to a far great degree, and for much longer, than they were. Keeping Jefferson fully in view helps remind us of this; holding him at arm’s length makes it too easy to believe the myth of universal principles naturally and gradually unfolding and expanding to include everyone. (Much the same could be said about the genocidal Andrew Jackson, the great champion of stealing land from the Indians to make it available to lower-class white homesteading farmers, though I find much more to admire in Jefferson than in Jackson.)
Moreover, Jefferson was an opportunistic federalist and strict constructionist, one whose own theories of constitutional interpretation most plausibly prohibited the Louisiana Purchase– and he knew it– yet for the sake of American power and expansion he went ahead with it. Again, that kind of contradiction is characteristically, almost constitutively, American. He was in principle in favor of laissez-faire economics, but harbored an agrarian distrust of cities, manufacturing, finance, and banks (very typically American) and pushed through a self-destructive embargo that required greatly expanded federal power to shut international commerce down. Likewise, the Kentucky and Virginia Resolutions vs. his later actions against the press as President. In both cases, the combination of (broadly) libertarian principle with opportunistic violations whenever “emergencies” arise (and they always do) seems to capture something important in American political life. And Jefferson often managed to moralize his own departures from principle into being new dictates of principle, such that he could still imagine his opponents as being venal and self-interested; what’s more typically American than that?
It seems to me that many of those who take Jefferson’s faults seriously then wrongly marginalize him. I’d prefer to take those faults seriously and still leave Jefferson in his central place in American historical narratives; those faults typically ended up deeply embedded American politics and thought. On slavery and race, the fact that he was worse than many of his contemporaries does not mean that he was worse than the subsequent American republic.