I don't think it was ok for Sherman to do what he did. It was uncalled for and unnecessary. He was already winning the war so why go and slash and burn everything. I think he might have wanted to put a good impression and show that he is powerful but theres was no need to do that. He could have focused on the war instead of doing pointless stuff.
I would compare this war to World War 2 because they basically destroyed stuff and people just like Shermans March.