Ahem. Argumentum ad populum, a.k.a. "10,000 Frenchmen can't be wrong." Appeal to motive in lieu of support, etc.
They'd have been wrong. He was not a "traitor", on the facts of his case.
Ahem, yourself. Williams says that current hostility to Lee is based on "presentism" or revisionism or modern relativism or whatever.
Pointing out that thousands of soldiers who fought against him and millions of civilians thought of him as a traitor disposes of his argument.
Whether they were right or wrong, that view isn't "presentist" or "revisionist."
Revisionism set in when people started to make some kind of national hero out of Lee after the war.
It's admirable that we're secure enough as a nation even to embrace people who want to split us up and weaken us, but that kind of magnanimity doesn't always provide us with the clearest or the most exact or the right judgments.