Licensing is not just a revenue mechanism - it brings accountability, or at least aids in administering the law if desired.  The police cannot identify a cyclist riding through red lights/stop signs/on sidewalks/with no hands while texting/not having proper lighting etc. because there is no plate by which to identify him/her.  The result has been a very apparent disregard of the rules of the road by a large marjority of cyclists which puts the safety of cyclists, pedestrians and other motorists at risk.