But I don’t want to downplay speed, as you noted it’s probably the key: most motorbike death are because speed or loose of control without involving any other vehicle. Also small cylinders (< 50cc) are almost absent in the death toll. If suicidal motorbikes with good helmet are allowed, so should be the bicyclists (with good helmet).
I think that's the logical line between e-bikes an electric motos: at what power or speed do you want to start requiring some kind of licensing or insurance?
Not sure how that works in the US but in France (and probably Europe?) everyone supposed to get a "civil responsibility insurance" that will cover many thinks including accidents on non-insured (legal) vehicle.
Maybe those should be more tightly regulated.
EBikes are popular and growing like crazy, especially outside the US. There’s somewhere over 30 million in India alone, estimated to double in five years. Their presence is not going away, even in the US, but it takes serious time and desire to get protected bike lanes built. Where I live there’s 6 grocery stores within 3 miles in either direction - and all on the other side of a 4 lane road. You end up riding in the road for part of the trip, and it’s more dangerous from relatively heavy traffic if you’re going 15 instead of 35 for even that short distance.