Of course not all of them, motor users do much more stupid things on roads, but a) they need to pass an exam and actually know the traffic laws; b) they can loose a driving license and pay high fines; c) they pay insurence and d) even when in accident, the chance of major injuries is radically lower than when riding a bike. Cyclists, on the other hand, don't give a shit and ride however they want. If we allow cyclist on roads, why not allow skateboarders or rollerbladers - what's the difference?