It's not just terrorists. Stalin, Saddam Hussein, Genghis Khan, and many of the ancient Romans didn't have that problem either. In the olden days, you didn't bother trying to tell insurgents and civilians apart; you just massacred the population until there wasn't anyone left who was willing to fight you.
Telling the difference between combatants and non-combatants only matters if you care whether or not non-combatants are killed.
This rather serious report should be of interest to LW. It argues that autonomous robotic weapons which can kill a human without an explicit command from a human operator ("Human-Out-Of-The-Loop" weapons) should be banned, at an international level.
(http://www.hrw.org/reports/2012/11/19/losing-humanity-0)