Like actually instituted mandatory confiscation? I don't think this is something that would even come close to happening in the 21st century, at least not until well after all our lifetimes, but yes I think there are enough crazies that this would start some actual shit. There's probably enough limp-dicks that say they'd get into a shootout then turn over their guns the instant a police officer came by. The MUCH bigger issue here would be that the police in the US would have to enforce this and they are by and large the same demographic that loves hoarding guns, you'd never be able to enforce it without getting the national guard involved and no way in hell any administration is going to want to try that. If they just banned assault weapons (which have been banned in recent history before), lowered magazine capacity, etc. without instituting any mandatory buybacks you'd probably hear a lot of inbreds threaten violence but I'd much more likely doubt that they would do anything.
Libertarians believe they're just victims of groupthink. Yes, the group thinks they're stupid, but not because of "groupthink." More like in the way the group thinks Georgia won the national championship last year.