I'm not convinced the red-light cameras are about enforcing the law. I have 2 major reasons for thinking this:
1. Red-light cameras are sold to governments as non-tax revenue sources. That means the purpose the politicians care about is raising money without dealing with the controversy of raising taxes.
2. The placement of red-light cameras, at least near where I live, correlates not with the locations with the highest violation of red light laws, but with the most politically powerless residents. In other words, you find the red light cameras all over the ghetto, but nowhere near the rich neighborhoods where people routinely take city streets at 45-50 mph.