Seriously? This is easily the worst argument against bicycles I see bought up again and again. Next time you're driving count how many people you see breaking the law be it bicycle, pedestrian or motor vehicle. Now count how many you see receiving fines/being talked to by the police.

But let's go ahead and agree with you and add number plates to bicycles - ignoring the huge costs incurred by the state - how exactly does that help enforce any laws? Bicycles are to small and light to trigger most red light cameras and to slow for speed cameras. So you're only left with visual enforcement by an officer of the law, which will have to physically stop the offender to issue any fines... which... o, hey... you don't need a number plate for that.