Sherman was a war criminal. Period.
And Confederate troops tended to execute black Union prisoners en masse when they could. Isn't that a "war crime"? Were Lemay and "Bomber" Harris war criminals? They burned out entire cities filled with civilian women and children.
I've known enough people with your outlook to understand you're not open to persuasion. But if Sherman was a "war criminal" then there will not be any generals in any war for whom the title couldn't be applied.