That's because he's NOT. I guarantee you that half the morons protesting his statue don't even know that he was an officer in the Union Army (US Army) before he was a Confederate. They probably think that he just woke up one day and boom...Confederate.
If they think he's evil, I'd like to know what they think of Oskar Schindler. He actually profited, for a time, off of Jewish slave labor for the Nazi regime, and he was, until Germany's surrender, a member of the Nazi Party.
I don't think Schindler was evil. Nor do I think General Lee is the American Anti-Christ that the Left is making him out to be. Of all the things that they could choose to focus on that were bad about the Civil War, Lee should not be one of them.