Well, in the US at least, the federal speed limit for an e-bike powered solely by its motor is 20mph, so to get past that would require at least some effort on the part of the rider - although I agree that’s still way too fast for sidewalks. I think maybe the first step then would be to improve the infrastructure for bike lanes; I use an e-bike to get to work when the weather is nice enough, and aside from that the single biggest deterrent to that is because several times I’ve almost been driven off the road by cars. Dedicated bike lanes with proper separation should reduce the amount of people biking on sidewalks, but of course there will always be someone doing things they aren’t supposed to.