there arent magic words/actions that can change his beliefs or get him to stop expressing them.
Giving him a bland response is the only way i get him to calm down after he starts himself up.
thats something you can work with. arguing with him only fuels it as youre seeing. bottom line, hes venting a bunch of out there stuff you dont want to hear. the goal is to keep yourself from being a target. there are lots of ways to do this, you know him and how he will respond best.
1. you can just listen and give bland responses. let him tire himself out and get it out of his system. thats a pain in the butt for you, but if hes not getting the response hes after, he may learn to stop looking for it from you.
2. when he slips into this stuff, especially if its relatively rare, you can have an excuse ready to get off the phone. you left something in the oven, you have to run to the restroom, whatever. politely, quickly, exit the conversation.
3. you can draw a hard line and refuse to discuss these things with him. he will push back and tell you what youve already heard. let him, be firm, and end the discussion whenever he brings these things up.
what do you think?