Not a cruel attitude only a realistic one. If you don't kill these guys they will return to kill you.
Once you have had someone try to kill you I can guarantee you will have a whole different outlook on this issue.
If this Marine made any mistake at all it was opening his mouth to someone outside his platoon.
One of the Iraqis tried to escape:
He said he also shot the man's partner, who tried to escape.
That being the case, the escaping Iraqi was not a Prisoner of War under control but still a combatant. The Marine had every right under U.S. Military Law to kill him.
The other Iraqi was another matter:
Covarrubias... found the soldier inside a nearby house with the grenade launcher by his side. Covarrubias said he ordered the man to stop and forced him to turn around. "I went behind him and shot him in the back of the head. Twice," Covarrubias told the Review-Journal.
That second Iraqi soldier was a Prisoner of War under control and was entitled to the rights of a Prisoner of War under U.S. Military Law. Such rights include not having his brains blown out for no reason other than anger.