I agree not to attack the person, any more than you'd attack them for stuttering. I think it's important to see this as a real mental disorder. I've been thinking about this in more depth. Think about some of these shocking conspiracy theories. You see many people across socio-economic lines, various education levels, single people, family people... it's all over. It's a human mental condition of some sort. If you have one of these annoying conspiracy fixations, it's going to start to define you to others, and that's likely to lead to typical loneliness and partial isolation. This is an uncomfortable thing to bear. And like starts grouping with like, even if only on some conspiracy forum online. Maybe an occasional regional meeting or book signing. People who share the particular delusion will clearly congregate, share and grow the delusion.
At this point, as I see this for what it really is, it's clear that arguing the facts isn't creating progress. It might be fun to wrestle and slap the guy around, but in the end this type of mentality can't be shamed into acceptance. There is an amazing amount of energy being deployed to protect the delusion, and systematically abandoning science to offer counter arguments. Anything to protect the delusion.
I find this fascinating all of a sudden.