"Doing so today would most likely bring an entirely justified charge of War Crimes against whatever commander ordered such attacks."
Maybe, but I wonder if those tactics might not still be required from time to time. It is necessary to subdue a bellicose population. I'd say the scale of subduction depends upon the enemy and the scale of the war. The piecemeal wars that we fight these days seem to lead only to more wars with the same exact people. And our enemies are always supported and goaded on by the same people. Is it possible that we're placing ourselves in a bad position by caring so much about enemy civilians?
Ditto that.
We do so because we cling to this romantic ideal that the poor, oppressed civilians are helpless under the tyrant's boot - when in most cases, a sizable percentage of the population supports the tyrant (in return for a share of the spoils) and is directly responsible for his enduring rule.
I don't think it's possible in most cases to "free" a people from tyranny. Once we are gone, spoils-seekers will put a new tyrant right back in power. The poor goatherds who at the bottom of society won't have a say in matters either way.
If a nation threatens us, we should reserve the right to utterly destroy their capability to wage war. Short of that, we can only be a good example - and we could start by focusing energy on removing some of our own Federal tyrant class.