> bikes and motorized treating busy sidewalks as special highways, which they use at speed

I'm always amazed more people aren't hurt in these situations. I can usually jump out of the way into the street, but what are people who can't do that supposed to do, just accept their fate?

And it bizarrely happens in places where there are good bike lanes. If it was "it's the street dodging cars, or sidewalk where you dodge me" I'd "get" it, but I'll see it right next to a protected bike lane.