Your right to speed is your ability to stop.
That rule applies to every mode of transport, including cycles, not just to trains.
I ride an e-bike: I've been out on it this morning and the battery is being recharged as I write. I'm now old and feeble, and the e-bike means that I can get up bridges and hills without having to get off and push. I also have panniers enabling me to carry more shopping.
The motor and battery make an e-bike more heavy and cumbersome than a pedal cycle. When braking that makes a big difference. From my experience with my e-bike, I think it is right that any cycle that provides power at speeds above 15 mph is a motorbike, requiring the rider to pass a test, wear a helmet, and use roads not cycle paths.
I only go above 15 mph when descending bridges. Anyone who wants to cycle faster than 15 mph on the level will be better with a pedal bike because it is much lighter. But in urban use, where there are pedestrians and other cyclists, going faster than 15 mph shows a lack of consideration for others.
Some of you will know that there have been 2 fatalities on the Cambridge Guided Busway, a cyclist and a pedestrian. Both fell into the path of a bus while avoiding a collision on the adjacent cycle track. That section of the Busway is now closed to buses. I have cycled that section of the busway: it is the fast moving cyclists that cause the danger, not the buses.