Once they pass a certain point it would be far too painful for them to admit that they, their friends, and everyone they trust have been part of the problem the whole time. It would destroy their psyche and wreck their lives. They have to believe that they're fighting a holy war because the alternative is unthinkable, and you'll never convince them otherwise because they're hanging on to this belief for dear life.
Understanding it just makes it that much more depressing.
I heard about this asshole on one of the local talk radio stations. It was treated as an "awww, isn't this eccentric" story, not a "this man is endangering everything and inviting a pandemic" story.