At least in the US you can't enforce it - and yes, any lunatic can grab a megaphone if they want.
The best way to handle problematic speech is more speech, NOT less. Trying to pretend lunatics don't exist is irrational and often a pretext to just block people that others disagree with. Screw that. Safest place for lunatics is out in the open, not driven underground.
If that were the case he would not be alone. There has been a mass conversion of libertarians to those sorts of views in the 20-teens. Many others converted to the far left. It feels as if libertarianism is dead.
I don’t really know. I’m just wondering if he still calls himself that.