You do if the local authorities say so. This is not done lightly, and you can disagree with it of course. But there was no violation of human rights here.
What happened was that the local authorities got informed that there would be a group wanting to do a surprise protest. They then set up a ban for protests for the day due to safety concerns. They did not believe there would be enough local police forces to handle this in a good way, due to them being busy at the actual protest sites already.
When the protesters arrived, police informed them that they were happy to escort them to the actual protest zones. The protesters refused. After that police rounded up the people in groups, not all at the same time due to limited capacity I'm guessing. As of this moment, one person is still being held - this person is accused of trying to push a journalist in front of a car.
I am all for protests. But in this situation I can understand the local authorities not wanting to run the risk also that things got out of hand. And if you allow this protest without the necessary police capacity, then what do you do when the other sides shows up and they clash?
I do think communication from local authorities failed in letting people know the ban, since it was all very last minute. That should have been handled better.