You go to war because you want an strategic outcome you can't get with other means. I doubt the strategic outcome of the USA in Irak or Afghanistan was "kill a lot, lose not that many, leave the country in shambles, achieve nothing in return".

The strategic outcome in both wars was to replace the goverment for a friendlier one, and in both cases the USA didn't get it, not even close.

But if you view wars as an sport where people kills other people and the winner is the one who kills better/more, then war is declared over and "teams" look for another war to "play", indeed USA won both wars in a walk.