Safety cameras aren't relevant in themselves. Whether the camera is there or not the speed limit is the same. If it's too low the right thing to do is to try to get it changed, and keep within it until then.

Hidden mobile cameras would make more sense than fixed ones. They could probably get away with fewer of them to achieve the same result - and spend the money on better signs indicating the speed limit, and warning that speed cameras are liable to be watching if we break it.

Brakes may have improved, but drivers haven't. However good the brakes are, they can't start working until the driver has applied them - and the faster the car, the more distance will have been covered in the meantime.