How do you feel about government setting up speed cameras at all of these side streets and issuing citations to all speeders, even those 1mph over the limit, through dragnet surveillance?
They'd have to collect a lot of tickets to justify the cost.
Are there really not more important things the legal system could be using it's resources to combat? There are child molesters and drug dealers out there.
The government is big and can do multiple things at once. Ensuring safe streets is an important responsibility. Vehicles kill many more people than child molesters and drug dealers combined.
I don't see anything fundamentally wrong with enforcing the speed limit in such a way. Perhaps one could question its efficiency, or the fact that many laws and regulations are enforced inconsistently based on the whims of whoever happens to be in charge. But those seem like small evils, relatively speaking.