I'm going about that my speed on my bicycle, much of the time. "Too slow for the road" has a meaning on the interstate highway. Someone who says that about city streets needs to go back to driver's ed. It's fine that the speed limit is 35mph. If you can drive that and safely pass slower traffic, do so. If you can't, slow down!

Perhaps the argument amounts to "driving a scooter on the road makes me feel unsafe, and I'd rather make others (pedestrians) unsafe to make myself feel safer." Seems typically selfish.

12mph is way too fast for a sidewalk. (Thus these scooter sharing startups will die.)

If an olympic athlete who runs at 12mph did his daily run on a sidewalk, people would be really, really angry. 12mph is fast. A police officer would stop him.

I disagree. Bikes aren't much faster .