So I don't buy the premise in the first place. In practice it's an authoritarian, abusive method.
If you have a legitimate reason to disperse people because elements are threatening violence, then disperse them - don't lock the those who are peaceful in with the violent elements.
This is more difficult than you expect. Police are drastically outnumbered in any crowd control situation. You can watch videos from Minneapolis riots where police just watch windows being smashed and shops being looted because they don’t have enough people.
It takes more than once officer to arrest someone too so things like Kettling need to be done for safety of everyone.
The rules are simple: if you get dispersion order it’s time to go. It’s not like they are not given a choice. I think a lot of people showing up to protests are just a bit unaware of the law. The number of times you see someone complaining about being asked to move on and they shout back that they are “on the sidewalk - can’t I just walk in my own city blah blah”. It’s just a misunderstanding of the law or a willingness to violate democratic law.
If you believe keeping everyone squashed together in a small space is safe, then you've basically admitted the crowd is not a risk to each other and can be contained, in which case there is not justification for it.
I don't care that the "rules are simple". Every authoritarian governments tends to have simple rules like that. That does not make this kind of authoritarian use of power justified.