Seems like most of the riders here are speaking from a recreational rider perspective and don't understand the utility rider's perspective. As in your bike is used for transportation, shopping and commuting. It has an actual job.
I'm the opposite. I do almost zero recreational riding. But recently as many have seen (I posted the pictures everywhere I could find a place to do so) I did a week's worth of daily and twice daily riding in a national park filled with ebikes. Nobody had a speed issue and the authorities didn't care. Again... filled with ebikes (so much so I was surprised) and this included a company that actively rented them by the literal truckload on the park grounds. Why no speed issues? Because nobody was going too fast for conditions. Everyone was enjoying the park. You want to thrill seek... you can do that on the hill in your neighborhood. You go to the natl park to see the sights. I am sure there are exceptions to this but they are so small in number as to be invisible. I can say for sure I was the fastest rider in the park... except for one guy on an analog bike who clearly lived inside the park grounds and was commuting.
To utility riding: Speed is important. More of it is better. You try relying on 15 mph bicycle speeds when instead you can ride at 30, with speeds limits posted at 35, 40, 45 and 50 mph for auto traffic along your route. If you are riding with things to do, places to go etc., halving your speed is a suggestion nobody who actually *rides* will care to listen to. This presupposes you build bikes whose components are up to this challenge, and contrary to ordinary consumer understanding, such components do exist and are perfectly effective. But they are expensive.
I am not a 'throttler'. I ride a bicycle so I can do assisted pedaling. And I gear the bicycle so that pedaling at those speeds requires effort that ranges from gentle to strong (as I see fit for the moment). But I also use a throttle regularly. It is after all an ebike and this is 2022. Why on a tool that is there to use would you handicap yourself? Like having a hammer but refusing to use the claw to pull nails out. Throttles for utility (read cargo) riders are regarded as essential by pretty much the entire assisted population. You use them to get up to speed. From a stop, I'm throttling from about a 2-one-thousand count from a dead stop. From there I accelerate and cruise via pedal assist. If I need to make a light and need just a boost ... throttle. Why would you not if the alternative is to scrub off all that momentum (and you're not breaking any laws or endangering your safety doing it)? Again its the right tool for the job.
As for law enforcement, the 30 mph number has been bandied about as the safe limit. Having bikes that cruise at this speed if desired, I can say that limit is about 34 mph with a loaded cargo bike on long, straight, smooth streets with a bike lane. I say that as thats about my limit on flat land if I am really working at it, and I have been both radar'd by motorcycle cops and paced by squad cars going that speed. And then they ignore me and move on. Remember I am presenting as a commuter rider, with steady and blinking rear and front lights, a downhill helmet with chin guard, and pedaling away as I go. If I was riding on some light motorcycle with pedals at 50 I'd be pulled over in a jiffy I am sure.
And none of this applies to riding on shared use paths. On those, given pedestrian intelligence and contrariness, sometimes 20 mph is double the safe speed. I have those in Monterey CA, where the paths are the preferred safe travel but my Class 3 + bike is dialed way back in gears and power for safety's sake. AND the electric-bicycle-mounted police don't give me any trouble.
Ebike regulation should be exactly what it is for autos: Behavior based. Put the elitism and the nosiness into other people's business in a drawer where it belongs. Act like a good citizen and be prepared to pay the consequences that already exist without any new bullshit regulations