My point is that the oppressed population who "lost" (Iraqis, Afghanistanis etc in these examples) aren't just like "oh well - I guess I'll just abandon everything I know and believe in and start eating beef and alcohol since the US invasion wiped out my country's military.". Instead they are resisting and so now you get the quagmire where basically anyone old enough to stand is now a threat to the occupiers even if they "wiped out" the army.
So you're not going to have some hypothetical "robot war" where no humans are hurt. The humans will start getting hurt once all the robots are dead.
I don't know if I would say "easy to crush". For Western nations i think it's especially hard because the images of civilian deaths have a large effect on the population and voting. Fighting asymmetric forces seems to always involve significant civilian casualties. Other nations operating without those constraints would have an easier time destroying asymmetric forces IMO. I think they would use the same tactics used for crushing dissenting civilians only kill-on-sight instead of at least the illusion of arrest-on-sight.
/not a military/war expert