Wrong. You can't win a game if you play by one set of rules and the other side has a different set.
As we kill more and more of them, the survivors just MIGHT be inspired to change their tactics. Otherwise, we give them the benefit of POW status, while they continue to slaughter prisoners, and there is no incentive to change. Killing terrorist prisoners is the only way to convince them to stop killing their prisoners. They started killing prisoners. When they stop, we will stop.