I've always felt like bicycle and foot traffic should be in the opposite direction of car traffic so they have a better idea of what's coming next.
People pulling out of side streets have to either merge into the first lane of traffic, or cross that lane and merge into the second (generally). If you have cyclists coming against the flow of traffic at sometimes 20mph, that driver now has to cross 2 lanes of traffic, and always at least one.
Car drivers rarely give cyclists space (in the US) as it is when traveling the same direction. How unnerving would that experience be when what was a 10/15/20 mph difference in passing speed effectively doubles (and then some)?