You, like a lot of Republicans, seem confused on this issue (I think El Presidente actually knows better, but just titled this thread for max troll).
No one (or, at least, very few--you can probably find someone to argue anything) is arguing that Lee was "evil" or "American Hitler." Removing his statues isn't as a direct condemnation of Lee himself, but as a condemnation of the Confederacy and the slave culture. It doesn't matter whether Lee, himself, was for or against slavery--what matters is that he took up arms against the US to protect the Confederacy and, by extension, their slave culture. By so doing, he's become a Confederate icon and when there's a push to remove monuments glorifying the Confederacy (removals being done by local mayors and governors), his statues are among those monuments.