I don't mean to be the dark figure in this conversation, but I think it's inevitable that robots will be used on the battlefield, just like people are going to continue to use cluster bombs, land mines, dum-dum bullets and other horrible devices. The reason is that they're effective.
War is a measurement of who is most effective at holding territory. It is often fought between uneven sides, for example the Iraqi army in their 40-year-old tanks going out against the American Apaches who promptly slaughtered them. Sometimes, there are seeming upsets but often there's an uneven balance behind the scenes there as well.
Robots are going to make it to the battlefield because they are effective not as killing machines, but as defensive machines. They're an improvement over land mines, actually. The reason for this is that you can programmatically define "defense" where offense is going to require more complexity.
Already South Korean is deploying robotic machine gun-equipped sentries on its border. Why put a human out there to die from sniper fire when you can have armored robots watching the whole border?
Eventually, robots may make it to offensive roles. I think this is more dubious because avoiding friendly fire is difficult, and using transponders just gives the enemy homing beacons. In the meantime, they'll make it to the battlefield, no matter how many teary people sign petitions and throw flowers at them.