Riders ride on the sidewalk because it's far more dangerous to ride on the street... cars are already not paying attention to bicyclists/motor cycles, are we to expect them to pay attention to scooters?
* Breaking traffic laws(blowing through stop signs)
* Riding in the streets and through intersections without paying attention to traffic
* Riding quickly through parking lots without paying attention to traffic
* Riding unsafely on sidewalks
* Riding without helmets
Generally, being oblivious to any safety responsibility. I witnessed a guy the other day riding down the sidewalk with one of those long skinny beer packs across the deck flopping around and sliding off with something else in his arms.
It's super stressful operating a vehicle around the hot spots with this erratic, illegal behavior going on however I have yet to witness a vehicle plow them.
As well, a scooter will casually accelerate very quickly up to 15mph which is not a casual cycling speed for most people; it's a beginner training speed and rarely seen in parking lots and other space constrained locations.
Lane splitting is not legal in my state, and scooters seem to be much more likely to zip between cars and between cars and curbs including through lights and stop signs. Typically, surprisingly, cyclists will actually full stop behind cars at lights and not go around them to the front.
I would contest, but be open to, it being a sampling biases. I would posit the scooter riders and my area are a much higher accident liability than cyclists in large part due to their own actions. Cycling is reasonably prevalent in the area I live at in my city.
I think I can sum it all up with one phrase: "Carte Blanche"
It also seems to me that Americans would be happier if every single sport activity had helmet. It is treated as something between magical make me safe item and moral requirement.
The statistics tell the story, and your brain is the number 1 thing you should worry about protecting. Just look at the long term impacts that even light concussions have in a sport like Football. You can seriously screw your life up in something like a scooter accident when you go down hard head-first onto concrete.
For #3, it's not that cycling is dangerous. It's that roads and car culture are dangerous. No activity exists in a vacuum.
And as for #1, the reason you wear a helmet is because the one time that you do fall headfirst onto concrete, the damage is life-long. It's not the frequency that you're protecting against, it's the inevitability of a fall and the potential lasting consequences.
And finally, I'd like to add that I'm speaking from a San Francisco point of view.
Even in a 15-30mph zone when a scooter rider blows out in front of a car with the right of way..
This is not a panacea, but there are some pretty good-seeming folding helmets out there: https://closca.com/products/fuga-helmet?variant=53832191509
The solution is better driving and riding training for both drivers and riders. Much of the riding skills taught in motorcycling classes are meant to increase the likelihood of drivers seeing the rider, and how to take percautions against inattentive drivers.
I doubt there are the resources to provide bicyclists and scooter riders the same training, and most probably don't want to shell out $50-$150 on a riding class. But that's really the only feasible solution.
American roads are extremely wide so there is plenty of space.