I'm not considering automobiles as inherently more "valid" participants of traffic than bicycles. I just consider any road where two types of vehicles of very different sizes which behave very differently to be an inherently unsafe and inefficient road for all participants. Obviously, the occupants of the larger vehicles are much safer in collisions with the smaller vehicles, but that's not my primary consideration. I just think the roads, or at the very least the lanes, should be dedicated to only bikes or only automobiles. Since there are far more automobiles than bicycles on most roads, if building new infrastructure is out of the question, I think it makes sense to not allow bikes to share the lanes. This isn't a condemnation of bicycle commuting, but rather a basic appeal to safety and organization, just like pedestrians are not allowed to share lanes with automobiles. The current situation on most roads, where a small number of small slow-moving bikes occupy lanes in the middle of a sea of automobiles, is just a disaster waiting to happen (and in big cities, it happens all the time).