I feel that the biggest threat to bike commuters are "loose cannon" cyclists...
I disagree. I don't believe that if a cyclist runs a light, that it justifies a lessened perception of motorists to treat all riders poorly. Before pointing the finger at others, lets see what we can each do to be better road ambassadors.
One thing I've felt has been helpful is to make eye contact with drivers (albeit with sunglasses on) and (in addition to the usual hand traffic signals) using large hand movements to indicate clearly what I intend to do (pointing, gesturing, holding a hand up to say "STOP", etc). Sometimes I shout if the driver is doing something stupid.
I drive a car too. There are times when I don't stop, such as when there is good visibility and no traffic. I'm guilty! And the same is true on the bike as well! If no one sees me, then who cares?
I agree with the other statement, regarding the truly incompetent: those riding without a helmet, riding against traffic, playing dodge 'em at the intersections. I figure Darwin's laws will take care of them...just a matter of time.