If you really want to engage with people like this, one good survival tactic is to ask simple questions. “How do you know that?” “Why would they do that?” “How can you be certain?” “Isn’t there a more plausible explanation?”
You might even catch them in logical fallacies or just clear contradictions. “But didn’t you just say the opposite?” “Wouldn’t it make more sense if …?”
A lot of them believe things without questioning it, so your questions could even help them snap out of it. Of course they could also get tired of your questions and end the conversation.