Robert E Lee was not Pro-Slavery he wanted "slaves " to have rights and treated them like employees. Ignorance is bliss.

Yes, your ignorance is bliss for you. The reality of the Lee's views:

When two of his slaves escaped and were recaptured, Lee either beat them himself or ordered the overseer to "lay it on well." Wesley Norris, one of the slaves who was whipped, recalled that “not satisfied with simply lacerating our naked flesh, Gen. Lee then ordered the overseer to thoroughly wash our backs with brine, which was done.”

not the only one

Just the biggest one:

Every state that seceded mentioned slavery as the cause in their declarations of secession. Lee’s beloved Virginia was no different, accusing the federal government of “perverting” its powers “not only to the injury of the people of Virginia, but to the oppression of the Southern Slaveholding States.” Lee’s decision to fight for the South can only be described as a choice to fight for the continued existence of human bondage in America—even though for the Union, it was not at first a war for emancipation.

https://www.theatlantic.com/politics/archive/2017/06/the-myth-of-the-kindly-general-lee/529038/