I appreciate the sentiment, but this would be what our enemy wishes. That would make their army much less likely to surrender; we want them to have a choice: surrender and live; fight and die.
This is the same tactic tried by the Fayadeen when they attacked under cover of a white flag. They hoped it would make us fire on white flags - the message they want to send to their own troops: "don't put up a white flag, they'll shoot you."