Junk Science
I have a number of family members who are easily snookered by junk science: alternative “medicine”, “proofs” of short-earth Creationism, and the like. If I thought they would actually listen to something as reasonable as The Seven Warning Signs of Bogus Science, I’d send them a link. But, alas, every attempt to dissuade them from such nonsense has been met with anger.
A discouragingly large percentage of people will convince themselves of anything if that belief makes them feel special, exclusive, and in-the-know. Cults survive this way, as do heretical beliefs in mainstream Christians denominations. When people attach their identity and their self-worth to being part of that belief system, and attempts to shine any light on inadequacies is considered a personal attack.