I think proving who the bad guy is is the hardest thing.
I watched a documentary the other night - they said the ragheads would fire from one building. To gain a better angle they would walk across the road in clear view of the Marines, enter another building and resume firing.
But - they had weapons stashed in all of the buildings, so they could walk around in clear view unarmed. And therefore not a “bad guy”.
Another one I watched quite awhile ago some soldier shot a guy but it wasn’t clear if he had a weapon or not. The soldier was freaking out, in the middle of a fire-fight, if he was going to get in trouble or not for killing the guy.
Rules of engagement should be: kill ‘em all, let God sort ‘em out.