The U.S. Marine Corps ran into a publicity problem recently when they accidentally sent a pressure group some documents on a cancelled project to develop a knock out gas" for riot control. The project was not making much progress, and the marines were apparently concerned that the use of such a gas, even if it worked,  would be condemned as chemical warfare. The same charge was made by the Chinese Communists during the Korean war, when U.S. troops used tear gas to force Chinese and North Korean troops out of bunkers and caves. While this was more humane than just killing them with explosives or a flame thrower, the Communists immediately saw the propaganda value and jumped on it. Many leftists insist to this day that America used chemical weapons in Korea. 

The marines have been in the forefront of developing non-lethal weapons, but there has been great reluctance to use them. Thats because there is no such thing as a non-lethal weapon, only less lethal weapons. Someone would do the world a favor by replacing the term non-lethal weapon with less-lethal weapon But because of the possibility that people would be injured or killed by non-lethal weapons, resulting in negative publicity, the military is reluctant to use them. An example of this is the recent Department of Defense order for $1.8 million worth of Taser guns. The high end version of the Taser gun costs about $400, while the cartridges are about $50 each. The Taser has range of 15 feet, which is far as the two wires from the gun reach. Two metal probes attach to the targets clothing and an electrical signal is sent that confuses the human nervous system. As a result, the victim is incapacitated for several minutes. Critics, however, claim (without proof) that at least fifty people have been killed by Tasers since 1999. The military purchase of the Tasers brought the bogus death stories out again, with the implication being that the troops had a new way to kill people. 

Non-lethal weapons are a nice sounding idea that few soldiers want to touch. Either because the weapons wont really disable to foe who is trying to kill you, or because the device might turn out to be lethal after all, and the media will go after you for being a war criminal.