He swore an oath as an officer in the Federal Army and reneged on that oath.
He had no obligation to "the South" (Lee thought the Confederacy ridiculous and criminal until Virginia seceded) and any obligation he had to Virginia would have been to ensure that it not continue to be led by demagogues down a path to its own destruction.
Lee is a cogent example of how sentimental attachments to myths and to prejudices (and I'm not talking about racial prejudices) can cloud an otherwise fine mind.
He properly resigned his commission. We forget today that the concept of loyalty to the country as a whole was one that didn’t come into being until post-war, and even that evolved over time. One’s loyalty was to that of their home state. I’m not going to re-debate the Civil War. My main point was what I said to the other fella, Lee alone couldn’t have stopped the Civil War had he accepted Lincoln’s offer. If he had turned against Virginia, he would’ve been considered the biggest traitor to the South, bar none, and his name would’ve been forever associated with the likes of Benedict Arnold. He knew that and that’s why he did what he did.
More than a few men whom would’ve preferred a different course of action were forced to have to choose sides. Moral superiority was not a province exclusive to the North as both sides had their fair share of wrong-headedness. The North, too, had demogogues, such as Massachusetts’ Charles Sumner. Unfortunately, in two diametrically opposed viewpoints, war is the only solution to reach its ultimate settlement.