Earlier quoted context omitted.
The problems were not the demonstrations, it was the barrage of death threats against Jews (inside France). Which were linked and exacerbated because of the demonstrations. The demonstrations themselves are acceptable - but the linked death threats definitely aren't, and unfortunately the state apparatus is not set up to deal adequately with the latter.
Can you expand on how the death threats were linked to the protests? I tend to think focusing on the threats themselves would be the better approach. Having trouble seeing how shutting down protest would help.
I don't know if you can conclusively prove they were directly linked, but we've seen how online people get radicalized by finding a community that espouses abhorrent ideas and then go on to commit crimes in service of that community. Real life gatherings and protests can have the same radicalizing effect in certain cases. That's not to say all of them do - the ideology behind the protest matters.
I agree that focusing on death threats would be a better approach - the problem is that it's very hard to find perpetrators and very easy to commit. Deterrence doesn't scale in that case.