This isn't the state monitoring people 24/7 though is it? It's enabling citizens to report a crime with evidence in a way they could for pretty much any other.
If you took a photo of someone using their phone behind the wheel and sent it to the police they might (probably not) investigate...
Whilst I sort of get what you are saying, I also think that speeding does appear to be one of the last bastions of dangerous/anti-social driving that people seem to think is acceptable. I have colleagues who boast and laugh about how they don't drop below 90 on their way into work on the A23...