That kind of sick slavery apologia is why we reject that kind of “ends never justify the means” moral outlook and why we look at the reality of a situation before passing judgement.
I know you're running hot after that one, but - didn't you mean "we reject ... ends never justify the means"?
Wait no, I just read back the thread again. You're saying that Sherman's march was justified, because it was pivotal in ending the Civil War with a Union win, and by extension, ending slavery in the US.
No. Sherman's march was not justified. It was horrible and cruel. When he decided to do it, and continue it, he lacked the hindsight that we enjoy. He could make some shorter term predictions, but nothing like being certain that it was necessary to end the war.
"But if it hadn't happened, or had failed, then the war may have turned out another way." That's an absurd thought experiment, because it didn't happen any other way. There is no "if."
The march happened, it was bad, historians now (with the benefit of hindsight) can point to the effects it did have (and historians don't always agree on everything or have complete and accurate information), the North won, slavery ended, which was good.
If the future ends justify the present means, that is license for anyone to do anything, with a clear conscience. And you never ever have to get to the stated end, even if it is your sincere belief, and even if your belief is in an empirically good thing.