It's absolutely a built-in hole in the human mind. Look at evolution denialism in the United States for a somewhat less morally offensive example of the same mental processes as Holocaust denialism. Or the anti-vaccination movement. The imperviousness to evidence or suasion is epic.

In the case of evolution denialism, it's wrapped in a socially-endorsed cloak of formal faith. In the case of anti-vaxxers, it's wrapped in a socially-endorsed cloak of 'protecting the children.' That's Irving's real complaint as cited above, that he doesn't have a socially-endorsed platform to stand on.