Studies have shown that most motor vehicle - bicycle collisions in urban environments occur in intersections.  That is one of the primary reasons that the Idaho Stop Law is so effective.  It allows bicyclists to clear the intersection instead of having an unsafe mass start. Why do you think they give pedestrians their own light in downtown Denver?  It's to reduce intersection interactions between motorists and pedestrians.  The same principle applies to bicycles.  

Also, it is very unsafe to mount and dismount a bicycle in traffic so the ride-walk-ride-walk scenario you presented is illusory.

The trouble with OP's type of comment is that it's so transparent.  People who single out the behaviors of bicyclists as if they are inherently worse than motorists and pedestrians are just engaging in ingroup/outgroup behavior.  It's completely unhelpful for creating safe public rights-of-way.