As a keen driver it pains me to admit I don't actually mind speed cameras. I certainly wouldn't want to be responsible for their introduction and I welcome the installation of every new one I encounter with the same level of enthusiasm as I would a pile of dog shit or piece of graffiti. But, I admit that they can be useful.
Used correctly they make school crossings, urban areas and dangerous roads safer places. If I fail to notice a nine-foot high yellow camera in plain view, chances are I wouldn't see a kid playing by the roadside either, and I think it would be fair to say I was too distracted, blind, unimaginative or stupid to be piloting a car-shaped missile.
The one problem cameras do cause, especially on faster roads like dual carriageways, is panic braking where drivers notice at the last minute and hit the brakes sharply, or brake automatically just because they've seen a camera. This often causes the following driver to increase the distance between themselves and the car in front so they brake too, and on a busy road the knock on effect of this is a chain of over-braking. If one driver isn't paying attention, or simply runs out of room because everyone has been driving too closely, someone gets rear ended.
I used to notice it regularly on the A14, where there are many cameras, causing the flow of traffic to repeatedly come to a stand still, and regular jams while the frequent accidents were cleared.
A new system of SPECs cameras which monitor average speed is operating on the A14 now and it has largely eliminated the stop/start issue and accidents are far less frequent. The camera partnerships probably don't make quite so much money but the A14 is a faster moving, safer bit of road to use.
Mobile camera units and hidden speed cameras on the other hand are the devil's work. I'm sure they make lots more money, but I see lots of panic braking and near misses as a result. Their occasional presence does not create a safer environment, they simply extract a toll for shutting the stable door once the horse has bolted.