All the Virginia Founders -- Jefferson, Washington, Lee -- were slaveholders. Tens of thousands of slaveholders supported the Patriot cause.
Contrary to Jaffa's mystic, metaphysical reading of the Declaration's equality clause, the Founders did not undertake the War of Independence with the aim of establishing universal social, economic or political equality. They wished only to free themselves and their states from British rule -- a very limited aim.
Jaffa pretends that self-government is incompatible with slavery. But both the Greeks (democracy) and Romans (republican) were slave-owning societies. And the American colonies had exercised local self-government for more than a century before the War of Independence, even while slavery flourished.
Jaffa, like others of his ilk, focus all their attention on a couple of dozen words in Jefferson's preamble, utterly ignoring the enumeration of specific grievances -- especially the indictments of the British for fostering servile insurrection and inciting the "Indian savages" -- which rather contradict the notion that the signers of the Declaration meant to usher in the universal brotherhood of man.
It seems to me that anti-Confederate conservatives like yourself (and Dr. Jaffa) are doing one of two things:
1. Intellectualizing a deeply held prejudice against the South; or
2. Seeking an historical pedigree for a "conservative" ideology that can embrace the civil rights revolution of the 1950s and '60s.
This second (and more likely) supposition points to a dividing line in the history of American conservatism. National Review, including Bill Buckley, opposed the civil rights movement from its inception; Barry Goldwater voted against the Civil Rights Act of 1964. What neo-cons are engaged in, metaphorically speaking, is an effort to draft Martin Luther King Jr. as a "conservative" icon. This is neither accurate nor fair, either to MLK or to conservatism.
It is worth noting that many Confederate leaders, among them Robert E. Lee, welcomed the abolition of slavery as a blessing. In the same way, many Southern conservatives welcomed the abolition of Jim Crow. But just as Lee never repudiated his stand for Southern independence, Southern conservatives feel no need to repudiate George Wallace ... or Jeff Davis.
Principle ought to count for something, and if the principles of conservatism include limited federal government and opposition to radical egalitarianism, then both Lee and Wallace ought to be counted as partisans of the conservative cause. Otherwise, one is required to construct some sort of "conservative" pedigree for Wendell Phillips and Stokely Carmichael.
My belief is that it is easier to admit the inconvenient fact than to attempt, dishonestly, to square the circle. Conservatives have, in the past, given their support to causes which are today viewed as immoral or unjust. So be it. But let us not pervert the meaning of conservatism in a public-relations campaign to convince liberals that conservatism and liberalism are the same thing.