Several years ago I had a scooter because I clumsily caught my foot getting off a stepstool and managed to sprain my ankle a couple days before our trip. I'm sure there were many people wondering wth I was doing on a scooter as there was no obvious sign I needed one. It was an eye-opening experience.
I'd agree that scooter incidents are a daily thing, but not all of them are the fault of the rider, and it's made me more aware of how I move in the parks. People coming to a dead stop with no warning right in front of you, people deciding that space you've left between your scooter and the group in front of you looks just PERFECT for them to squeeze between, and my favorite, the guy on a phone who came running out of a store without looking and plowed right into me.
No doubt grandma on a scooter can cause a problem (although grandma probably DOES need one), and no doubt there are people who are using them for convenience rather than need. But the lion's share? Not sure anyone is really in a place to make that judgement. And honestly, I don't recall seeing a huge number of morbidly obese children riding scooters at
Disneyland.