"No noise" is certainly not clear-cut. It may seem that way from any subjective perspective of what counts as noise, and it can seem so obviously right, but it's certainly not objective or universal. Which, I believe, is part of the point of the post.

Apart from that, let me give a real-world example of how clear-cut things become not so clear-cut, from a legal or rules point of view. Where I live, vehicles and other means of traffic used to be clearly divided into categories:

- Cars are, well, cars

- A motorcycle is a motorized two-wheeled vehicle with an engine displacement greater than 50 cubic centimetres or with a maximum speed of more than 45 km/h

- A moped is a motorized two-wheeled vehicle with both engine displacement and maximum speed less than above. (It's still a motorized vehicle but the legislation is somewhat laxer in parts due to lower power and speed.)

- A bicycle is a non-motorized, human-powered vehicle with at least two wheels

- Roller skates, skateboards, kick scooters etc. are not considered vehicles, so any person travelling on them is considered a pedestrian.

There may have been some other categories but you get the general idea.

Cars and motorcycles aren't allowed on bike paths. That would also include parks. Mopeds may be allowed on bike paths by an explicit sign, although you aren't likely to see one on a park path.

Then someone comes up with the electric bicycle.

Since the bicycle is defined as non-motorized, and an electric bike clearly has a motor, does it count as a bicycle or a moped? Is it allowed on bike paths? Or in parks?

It's not entirely an academic matter of definitions either. An e-bike running 30 or 35 km/h may not be fast enough to ride on the street among car traffic, and most people probably wouldn't be comfortable riding one there. Also, it's slow enough that most car drivers probably wouldn't want those in the street. But in addition to being motorized by definition, such an e-bike might also be practically kind of fast for urban bicycle paths. People on bicycle paths started feeling uncomfortable with e-bikes zooming by, not to mention pedestrians on shared pedestrian/bike paths.

So, where do e-bikes belong? Where are they allowed?

And once you've solved that one way or another, someone comes up with the electric scooter. Their speed may also vary from somewhat faster than walking speed to something resembling fast e-bikes. Is the person riding one a pedestrian? A bicyclist, similarly to e-bikes? Is the vehicle a moped instead? Should you be allowed to ride an electric scooter going 30 km/h in a park? One with a maximum speed of 25 km/h? If not, what about the lycra-wearing dude on a bike going upwards of 30 km/h?

If all of the above are allowed, why aren't mopeds or motorbikes if they stick to riding no more than 30 km/h? Because of the noise? What if they're electric?

And this is while still staying reasonably objective. If the electric bicyclist or scooter rider is disallowed from parks or bike paths but a road cyclist going over 30 km/h is allowed, in some significant number of people that's going to spark a sense of unfairness. If their views aren't heard, that can lead to resentment. Some of the people who don't care for any two-wheeled vehicles and who just want to enjoy a stroll don't want to be scared by anyone going too fast.

What should or shouldn't be allowed, or indeed what's reasonable and what isn't, definitely isn't clear-cut in a sense that people in general can agree on.

Forum or social media moderation is certainly going to be a lot more up to interpretation than that depending on people's values, personal experiences, context, etc.