He's a peer. We both hold the same job title, do the same tasks, etc.
see edit but basically, in this sort of scenario, I do wonder how much it would hurt just to agree with him. My book club always had waaaay better conversations when everyone disagreed or had different opinions. We found that it was harder to talk about novels we were all in agreement on. Hmm?
If I'm being brutally, brutally honest. I think agreeing with him would hurt my image with my other co-workers because I know some make fun of him for believing in this stuff (to be fair, we all poke fun at eachother for various things, from height to enjoying professional wrestling to playing too many video games) and I don't want to be thought of as someone who believes in that stuff too. At the same time, and this is part of the reason why I find the conversations so weird and uncomfortable, is that I find the ideas so against reasonableness that I find them distasteful to say the least. I feel like agreeing with him just to placate him as wrong.
Have you tried just saying "cool" and changing the subject ? You aren't going to change that type of persons opinion, they probably need to believe in the crap for some weird reason. You might have dug yourself in too deep for this trick though since you've engaged him in the conversations before.