I know someone who withdrew from a club, just because the leader and sidekicks kept banging on about lefty crap, totally unprompted.
Most don't even know they're doing it, they think it's normal conversation they're so up themselves.
It's often done to sniff people out - to find out whether they're one of us or not. It's tiresome. I suspect some weaker people actually pretend to be believers, many just say nothing while getting quietly annoyed, only a small number actually tackle them head-on. Many just say balls to them, make an excuse and find other people to spend their time with.
The net result of most people not confronting them is that this tiny minority of nutters actually start to believe they're the majority. Then an opinion poll shows 14% support for labour, they all think it must be wrong because everyone appears to agree with their tiresome lectures they inflict on those around them.