Bunny's initial comment:
If you were in NYC and had heart stopping experiences with bikers going through red lights, against traffic and on the sidewalk you might think differently. They should have a license so they can be identified and fined for not following the rules of the road.
My response was a little too flip, basically a rehash of some of my earlier arguments which boil down to the idea that most of those cyclists wouldn't bother to register/tag their bikes. My dislike for licensing and registration schemes of most types stems from my dislike of governmental intrusion into my life, and in this case I looked at the issue only from my perspective. I am a vehicular cyclist and I follow the rules of the road. Because I follow existing rules I don't see why I should have to put up with additional restrictions/regulations. Thinking about it after reading Bunny's comments and emails brought something else to mind:
Cars have to have plates on them, so requiring the same from cyclists isn't adding restrictions, it's bringing cyclists into greater parity with motor vehicles.
This is something I need to think about a little more, but at the minimum I am willing to recognize that I was wrong about bike licensing, and in some jurisdictions (those with large populations of scofflaw cyclists) putting plates on bikes might be a legitimate way to discourage inappropriate behavior.