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)
and landmines, if you're looking for precedent.
Neither land mines nor pit-traps are "autonomous robotic weapons" of course. But speaking of precedent, there are numerous campaigns to ban land mines (eg. http://www.icbl.org/), for reasons which are rather similar to those advanced in "The Case against Killer Robots".