I think there is a subtlety here.

I believe that forms of protest that inconvenience the public should both happen, and be illegal.

What that means is that a significant mass of people is then required.

If you have ten or twenty people walking slowly down a road and as a result tens of thousands of people are inconvenienced then obviously the police should step in. If they don't, then members of the public will do instead, as we've seen.

If an issue is actually important enough then you'll be able to recruit enough people that they won't be removable without resorting to extreme force anyway. In that case the protest is far more likely to be for a legitimate cause.