Loudly and visibly changing the rules doesn't "create offenders". Offenders aren't victims of changed rules.

It has been shown time and again that lowering speed limits in cities reduces traffic accidents and emissions at close to no costs to the flow of traffic.

My own city (in Germany, so it really was a heavily-criticized decision) lowered the speed limit on one of the major arterial roads to 30 kph. It is one I have to use regularly, and oh boy, let me tell you: I was soooo opposed to the change. Yet, it really only changed how fast you arrive at the next red light. There is literally no discernable change in how long it takes to pass that street, especially during rush hour. Traffic just got a little more fluid.

It is, however, the street with the most speeding tickets in town. I regularly see one or two mobile speed cameras along the way. And I've never been fined. You got to wonder...