In Afghanistan? Unlikely to be hundreds of thousands of civilians killed by Americans/allies. https://watson.brown.edu/costsofwar/costs/human/civilians/af... says "at least 71,000 civilians killed" and many of those would have been killed by other side(s).

"Justified"? Probably not, but we'd have to determine what alternative actions America/allies should have taken instead and compare.

I mean, "avoid all US-caused civilian deaths by letting AQ continue to operate from Afghanistan with impunity after 9/11" would not obviously have been the right thing to do.