They aren't cyclists -- they are motorists using illegal uninsured vehicles.

[In the UK, electrically assisted pedal cycles must cut out after 15.5 mph; the max motor output is 250 W; and the motor must solely be activated by the action of turning the pedals; vehicles that don't comply with these rules are illegal]

This kinda feels like a no true Scotsman, if it walks quacks and flies like a duck it doesn't matter.

Edit: I say this a cyclist myself. I see other people on bikes do some dumb shit, we can't say they aren't real cyclists because they do something that makes us look bad.

I am a cycling idealist and I struggle with outcasting a group.

However, e-bikes can give unconditioned people “superhuman” strength and endurance. Physical training tends to give individuals intuitive limits for personal safety, but using a modified e-bike short-circuits this intuition.

I am thinking that limits on stuff like diameter of frame tubing or tire width (which would not stand up to riding at speeds outside of normal “human” parameters) can help.

They can't help. My friend sells second hand bicycles recovered from the police. A couple of weeks ago they gave him an e-bike. This thing had been modified with a twist throttle, 1 kW motor and a maximum speed of 62 MPH.

He took it up to 40 MPH (on his own private land) before chickening out. The chain would simply not stay on the cassette at that speed. He reckons that if you did drive it to the limit, you'd go through a brand new set of disc brakes and calipers in a week, if you didn't manage to boil half the hydraulic fluid off in the mean time!

But to a non expert this thing looks exactly like a regular bicycle--because it is (or was, before it was illegally modified to be a motorbike).

E-bikes are sometimes tough to reason about because they’re both bicycle and motorized vehicle. This breaks the duck analogy though: they only look like a duck, but they do not quack or walk or fly like one.

I like e-bikes, they are getting more people to ride bicycles, and I’m especially seeing a surge in older people getting out and riding far. This is a good thing for all cyclists. But parent is correct: e-bikes are motorized vehicles. There are bicycle trails where I live where motorized vehicles are not allowed, and that includes e-bikes, and it is enforced.

Other replies have made the point that they look like, but don't quack like ducks. I just wanted to point out that I was speaking from a legal perspective: specifically, "[those] who uncapped their limiters and installed 1000 W motors for their “sleeper” builds" are motorists, and they are prosecuted as such when caught (which is not often, because cuts to police, CPS, courts and legal aid have effectively decriminalized most crimes in the UK).

You have identified that they give cyclists a bad reputation, and we all suffer due to it. :(

It doesn't fly like a duck, that's the point. It flies like a cyberduck with a rocket pack.

Cyclists who behave badly are cyclists. People riding vehicles with motors that let them go that fast simply aren't cyclists. We don't call ICE motorcycle riders "cyclists" in that sense either.

Legally speaking they're not cyclists though.

On my daily commute, I've now had a chance to observe the same e-cyclists several times through the summer months. I tend to notice and recognize bikes and cyclists because I'm interested in cycling. I think a lot of the behavior that folks are noticing, such as "it seems like e-bikes don't have brakes" is due to inexperience and residual car driving habits such as accelerating out of congestion.