No one is saying “all these civilian casualties are ok”, stop oversimplifilying the situation.
I know it’s tempting to make blanket statements about moral imperatives from your armchair, religion has been doing that to us for centuries, but it turns out the real world is actually full of moral dilemmas, where there IS no outcome where no one dies, and all you can do is pick the least bad option.
“All civilian casualties are inadmissible” is the coldest of cold takes, right there next to, “well I don’t think anyone should have a war at all!” Like, great, thanks, why didn’t anyone think of that?