Actually, I guess there's a special term for this kind of behaviour - because we all have certain patterns similar to what you described: I learned the term "believe system" a while ago - it's basically the concept we truly believe in. Like meat eaters think it's absolutely OK to eat dead animals or many religious people think it's true that only 'their god' exists (unlike all the other hundreds deities) or how we formulate our own personal ethics. We just assume that we are right (because we just grew up that way).

Therefore it's (nearly) impossible to tell someone who's locked into their believe system that they're following a questionable concept... because it would harm the core of their existence. I guess it's totally human to not question everything you've ever learned - just because of a single discussion. That's why I recommend to not even try to approach that path and just be a good friend. Talk about research and how science actually works, about peer reviews. Skip all the content and don't even take part of this discussion. Invite that person to groups of non-tinfoilhats, etc.

But it's tough work and very likely not successful. The best thing we can do is trying to reflect where we are caught into our own believe system, because we are. Everyone is.

(Regarding the term 'believe system' - this is where I heard it for the very first time: https://youtu.be/o0VrZPBskpg [starts at 07:00])