This topic interests me greatly because I have lost a few friends over this sort of thing. I’m not sure how close the friend is from the OP, so this may be different. My situations are more casual friends. One of them was my state representative, fortunately he did not run for re-election. The problem with not bringing up the subject is that they keep doing it. Actually, it is several topics. We’ll be talking about the weather, then suddenly I’m questioned what I think about 9/11 or flouride, and if I don’t the answer right, I get a lecture.
Since I’ve been the one adjusting his world view lately, I think I’m the one noticing it. As I increase my critical thinking skills, more things have become CT to me.
My solution, which has yet to get much testing, has been to study the history of Western Philosophy. Hume, Bertrand Russell and Karl Popper have been good sources to help me understand just what it means to be liberal, to think like a modern person, and to apply the scientific method. One of the more important principles is the Principle of Charity, try as hard as you can to accept that the person giving you information you disagree with is not crazy. If you can’t answer every challenge, ask for time to look into it, and give them time if you present them with new info.
Remembering a few key logical fallacies can help a lot too. If I do know about what they are saying, and I give them solid answers to their questions, often the conversation ends with “there are just too many questions.” Depending on how gentle you need to be with the person, you can either simply say that’s not a reason to continue to believe something, or offer to give them more backup to whatever answer they need. If they refuse to accept your sources, then you’re getting into someone being unreasonable. That can strain a friendship. With one, it is not so much about his ideas anymore as I just can’t let someone call me stupid while sitting down for coffee and continue to call them friend.
To end on more positive note, I tried turning the question around to someone recently. It was about some farmer claiming the FBI destroyed his GMO research. I asked, why do you believe the account of this guy from Indiana that you’ve never met? His response was fairly contrite.