I would disagree - I was reading about one chap who painted a Smartie pack black and stuck it to his helmet - He noticed a marked change in attitude from drivers.
But even if you don't believe that - cameras can and do result in convictions, which can remove said driver from the road, which is only a good thing if you ask me.
Now I don't have a camera, not that interested in getting one. Out in lazy Norwich I don't feel its justified, but I have cycled in London, and no question Id buy one if I lived there!