Bicycles are not able to maintain the speed limit, so they force traffic jams as cars wait to pass. Cyclists often don't (or aren't required to) obey the same laws that apply to cars, so they blow stop signs/lights and cut across lanes, forcing drivers to slam on their brakes to avoid hitting them. Bike lanes cut into valuable space for extra lanes that should be used for automobiles.

In my mind, bicycles fall into two categories: 1) Exercise equipment - Ride on a track or on private property. 2) Off-road vehicles - Go ride in the desert, the mountains, whatever you enjoy. Don't ride on public roads and interfere with cars.