There is an entire category of e-bikes that are officially sold for off road riding, whose top speed may be 25mph (and higher in some cases or with trivial mods). And in more urban and suburban areas they are commonly used on sidewalks and roads (their top speed is approximately the same as some road speed limits). They can be a danger to others, and to the riders (who commonly don't wear helmets). I have personally seen them racing around a school yard park (technically after school hours, but some children are still playing). It may not be the fault of the e-bike that the riders are not doing the right thing, but catching (and citing) the riders is hard, so forcing additional performance limits and registration may be the only way forward. All part of the "This is why we can't have nice things" world (it only take a few people to ruin it for everyone).