The U.S. Air Force recently released a report (Unmanned Aircraft Systems Flight Plan 2009-2047) in which they predicted the eventual availability of flight control software that would enable UAVs to seek out and attack targets without human intervention. This alarms many people, who don't realize that this kind of software has been in service for decades.
It all began towards the end of World War II, when "smart torpedoes" first appeared. These weapons had sensors that homed in on sound of surface ships. Another type detected the wake of a ship, and followed until it's magnetic fuze detected that it was underneath the ship, and detonated the warhead. The acoustic homing torpedoes saw use before the war ended, but the wake homers were perfected and put into service (by Russia) after the war ended.
Another post-war development was the "smart mine." This was a naval mine that lay on the bottom, in shallow coastal waters. The mine has sensors that detect noise, pressure and metal. With these three sensors, the mine can be programmed to only detonate when certain types of ships pass overhead. Thus with both the smart mines and torpedoes, once you deploy them, the weapons are on their own, to seek out and destroy a target. These weapons were not alarming to the general public, but aircraft that do the same thing are.
However, smart airborne weapons have also been in use for decades. The most common is the cruise missile, which is given a target location, and then flies off to find and destroy the target. Again, not too scary. But a UAV that uses the same technology as smart mines (sensors that find and software that selects, a target to attack) is alarming. What scares people is that they don't trust software. Given the experience most of us have with software, that's a reasonable fear.
But the military operates in a unique environment. Death is an ever-present danger. Friendly fire occurs far more than people realize (or even the military will admit). Combat troops were reluctant to talk about friendly fire (mainly because of guilt and PTSD), even among themselves, and the military had a hard time collecting data on the subject. After making a considerable effort (several times after World War II), it was concluded that up to 20 percent of American casualties were from friendly fire. So military people and civilians have a different attitude towards robotic killing machines. If these smart UAVs bring victory more quickly, then fewer friendly troops will be killed (by friendly or hostile fire). Civilians are more concerned about the unintentional death of civilians, or friendly troops. Civilians don't appreciate, as much as the troops do, the need to use "maximum violence" (a military term) to win the battle as quickly as possible.
The air force has good reason to believe that they can develop reliable software for autonomous armed UAVs. The air force, and the aviation industry in general, has already developed highly complex, and reliable software for operating aircraft. For example, there has been automatic landing software in use for over a decade. Flight control software handles many more mundane functions, like dealing with common in-flight problems. This kind of software makes it possible for difficult (impossible, in the case of the F-117) to fly military aircraft to be controlled by a pilot. Weapons guidance systems have long used target recognition systems that work with a pattern recognition library that enables many different targets to be identified, and certain ones to be attacked. To air force developers, autonomous armed UAVs that can be trusted to kill enemy troops, and not civilians or friendly ones, are not extraordinary, but the next stop in a long line of software developments.