Statistically the best thing for cyclist safety is increasing the number of cyclists on the roads. So any safety rules that decrease the number of cyclists (like requiring a license) has to be offset against the increased risk caused by having less cyclists. This is the reason that mandatory helmet use makes roads less safe for cyclists.

The other aspect is that you still have pedestrians, who may have little or no knowledge of road safety, so you still have to train drivers to be extremely careful regardless.