I don't know about Oakland, but in Boston these wouldn't be legal to ride on the sidewalk. Hell, they're barely legal to ride in the bike lane (only motorized vehicles that can't exceed 35 mph and that make a motor smaller than a certain size). Combine that with the fact that most riders won't be wearing helmets and it's a potentially deadly accident waiting to happen.
For the curious, the maximum motor size to ride in the bike lanes in Boston is 50cc.
cc is a measurement of displacement, only useful for combustion engines.
Equivalent for electric motors would be Wattage.
it is not legal to ride them on the sidewalk here (neither are bikes legal to ride on the sidewalk) but I see it everyday now -- with folks yelling "get out of my way"
Well off course, anything near a road is deadly. Just standing on the side of the road can be deadly. Anything around cars at all is incredibly dangerous. It is absolutely insane we allow cars anywhere near people.