If it's necessary to win a fight that matters, and it works, it is okay.
See: allied bombing campaigns in WW2 wherein we intentionally roasted thousands of babies and grandmas.
The self-indulgent alternative is a recipe for extinction. And you can't have much influence over the world if you're not there.
If you're not brutal enough, you just end up handing the future to someone more brutal, which is itself a wrong. Just like it'd be wrong to let the Nazis take Europe because you didn't want to roast babies and grandmas.