I'll beg to differ... Stanley Park in Vancouver is an example. Stanley Park Drive is an automobile path but running alongside it is the Seawall, a bike and separated pedestrian path. In many sections the path is too narrow to pass, due to a cliff face. They've improved it somewhat in the last couple years, but I think very fast riders still prefer going on the car path so that they don't have to wait to pass people on rented bikes going slowly trying to simply take in the park.

I do think fast cyclists should be able to select their risk level and speed, though speed limits should be no more than 40km/h (25mph) to even begin considering a road to be a safe path for cycling.