It varies slightly by state, but many places you can have up to 750-1000 watts and up to 20mph unassisted on flat ground and still have a bicycle, meaning no license or insurance requirement. You'll typically pedal close to 20mph on flat ground. I find these limits to be reasonable.

Tell that to the guys riding them.

I beginning to see a few on the local multi-use trail (where motorized vehicles are banned). One even has a giant fairing and looks more like a tuk-tuk or e-car than a bicycle.

Right now, there are few enough that it's not a big problem. But, the tuk-tuk e-bike is larger than a normal bike, so it's hard to pass (or make a pass) and will do more damage in a collision. Some of them are faster than the average road bike - I've seen several hybrid-style e-bikes cruising at close to 20mph with the rider soft-pedaling.

It's a can of worms for sure.

You've hit the nail on the head. To a lot of people (myself included), they're more like electric motorcycles.

I don't really care if people choose to ride them, but there are already designated trails that allow motorized access, and poaching mountain bike trails is going to ruin it for everybody.

In europe they are still allowed everywhere if they are constructed as a pedelec with a top speed restriction.