“Stochastic terrorism” is free speech.
I get it, you don’t like your enemies and you want to find a way to punish them. Maybe even to prevent them from saying things that seem to be increasing their base of support. So you find a few dangerous whackos who also happened to articulate the same points that you’re trying to suppress. Boom, instant justification to suppress that speech! Even if the speech isn’t per se illegal, maybe the fact that both your target and the whackos said the same thing makes it ok to suppress that speech anyway!
No, that doesn’t make it ok. Free speech is free speech. Stop trying to unconstitutionally suppress the rights of your opponents.