Social movements don’t just happen from grassroots these days. They’re seeded by foreign states. A simpler solution would be require ids for social media posting. If you don’t provide an id you get a limited number of views.
And I don’t see anything wrong with a preventative system in principle, we should be able to join up social services information with policing, because we have had cases where a mass murderer has been known to multiple services.
Edit: probably not ids but a token that verifies my nationality would be enough.