Eventually, in the classic fashion of The Zealot, they get so emotionally wrapped up in their opinions, that not only will facts not change their mind, they will attack those who brought the facts to the foreground, and eventually, they feel morally superior, and once they claim the moral high ground, well, their ego is completely wrapped up in being right, no matter what.
sounds like Hitler......oops...I said the evil word...must be contagious.......LOL