Drivers tend to see cyclists as intruders, and fail to give them the space and respect that they give other “legitimate” vehicles. The bike lobby exists to combat this. Things like Critical Mass rides, signage, and road paint are all about changing driver psychology and raising awareness about a cyclist’s right to occupy the travel lane. If you’re going around saying car and cycle traffic should not mix, you are its avowed enemy, same as the SUV drivers shouting at bikes to get out of the way.

Even very serious and activist cyclists around here are still most likely seasonal/recreational riders, and still want to use their cars, at least in the winter. (See “share the road” bumper stickers). They are not necessarily wild about reducing vehicle access.