I live in Tempe, AZ near ASU - one of the "most bike friendly" cities in the US, and I can't tell you how many times I've been nearly killed by a bike at full speed weaving in and out of pedestrian traffic on the sidewalk - where it's actually illegal for them to ride.
Bikes do not belong on the sidewalk unless they're moving as slow as a pedestrian, which they never are. They're a hazard.
Many years ago I biked daily on 40 mph city streets, so I'd like to think I know what I'm talking about.