Cutting through the mythology that has built up around Forrest is quite a task - it's true that most people who dislike or even hate this general cite Ft Pillow, KKK and slave trading. For many, that's enough. So, it should be the same thing with Sherman. He was famously biased against blacks - didn't want them in his army and grumbled about Massachusetts using blacks to fill their quotas. He believed they could not be soldiers and shouldn't be used as bullet stoppers for whites. He said, "The n-r is an excellent fellow, as such. But he is not fit to vote with, live with, marry with or associate with me or mine!" The Knights of the Golden Circle thought he was their poster boy - he turned down their offer of membership. We have that nightmarish incident at Ebenezer Creek. Ellen, the wife, was trying to set up housekeeping in Louisiana and complained to her husband about a lack of good help - his response was he guessed they'd have to buy a n-r! We won't even mention Sherman's overall Indian policy...
Well, let's see about Forrest. After he began to understand the old South was gone forever, his racial attitudes began to change. He supported black education, voting rights, businesses, and opposed segregation. Not that he didn't have some ulterior motives - he knew the black vote was necessary to restoring Democrats to power in Tennessee. Got to make friends amongst the coloreds! But it did go further than that. After his health deteriorated to the point any political ambitions he might have had were over and he was reasonably out of that area, and the Democrats were back in power, he still supported black rights and all of that. Why 'pretend' any more if your objectives have been achieved and you're no longer in that field? And, Forrest knew better than Sherman that black men could indeed make good soldiers. He fought enough of them at the end and was beaten by them at least once. He may not have admitted it - at least not out loud - but he knew it anyway. And that meant a whole lot of things that he had believed all his life about the blacks was completely wrong.
The question has been asked why like this messy guy? He's not hero material. (He wasn't messy until others found various reasons to muss him up, incidentally.) That's kind of like asking why like any of the rebel generals - they rebelled, they owned slaves, they were...a lot like Forrest. But lots of us have our favorite rebels, don't we? It doesn't mean you support somebody's ideas just because you find them fascinating. (And, no, it's not something about liking the 'bad boys' - that's trivializing the subject.) I find Napoleon fascinating, too, but that doesn't mean I view him as a hero. Forrest is, as Sherman succinctly noted, one of the most remarkable men our CW produced. He still is.