How can one ostracize a dead person?
Curiously, one does not read where the self-righteous detractors of Robert E. Lee, who did not own slaves, have the consistency to denounce the Patriarchs in the Bible, who did.
Could there ever, possibly, sometime in the universe, conceivably be a scenario wherein someone could point out something about Lee without them being either "self-righteous" or a "detractor" (or both)? BTW: Lee did own slaves.
Can you cite a source for Lee owning slaves? Regardless, even if he did, so what? Many of America's Founding Fathers were also slaveowners, including Washington and Jefferson. If you're going to be consistent, I suppose you should join the Left in condemning the United States at its founding if you're going to condemn the Confederacy. Alternatively, you could be consistent in the more reasonable way and acknowledge that it's possible for an honorable man to be a slave owner or to support the legal rights of slave owners, whether it was in 1776 or in 1861.
Of course, slavery is not part of an optimal system. But the point is that accepting it as part of an existing culture or economy does not discredit one's arguments on other issues--such as some of those that were also in play in the period that you have chosen for your strident insults.