Two problems with that.
1: Not all civilians could leave. Many didn't have a place to which to go, some didn't have any means to get there. And those that couldn't risked having their homes bombed and getting shot.
2: Killing or sending to Abu Ghraib all military aged men is barbaric, worthy of the Third Reich, not done by civilized societies.
Repeat, barbaric, reminiscent of the Crusades, Asian hordes and the like. Not a tactic for a country trying to win hearts and minds, for sure. It is a tactic designed to create people who hate you, who will try to kill you later.
Arf