I'm too tired to find the cite now, but Car and Driver has done numerous articles on this subject. In fact, the contractors who run red-light camera systems have sometimes prevailed on authorities to reduce yellow-light durations on camera-equipped intersections to increase the violation rate.
These systems are usually run by contractors, who include a guaranteed-revenue clause in their operating agreements. If the cameras are actually effective in stopping people from running red lights, then the operators will go back to the local government to demand that they make up the shortfall.
All in all, a dirty business that's clearly not safety-driven.