I like when people say "but the enemy did this and that, so us doing something similar is totally fine", because it is just false. But going to "we already did it once, so no biggy if we do it again right?" is even better. It acknowledges, and defends, the evilness of killing civilians at large scale at the same time. Kind of like wanting to be a big, badass and still feeling the need to morally justify all the shit one does.