It's rather obtuse to think that brilliant people can't be mentally ill. John Forbes Nash comes to mind, as do Hemmingway, Winston Churchill, Abraham Lincoln, Vincent van Gogh, for starters. Many creative, intelligent people have mental problems.
That having been said, is it delusional for Mr./Mrs Neumann to keep their daughter from getting medical attention because they believe Satan is afoot and only God can oust the evil? Yeah, and even most religious people would condemn that. The same people who think that if they pray hard enough with a group of businessmen, God will take time out of his busy schedge to smile upon them and their fiscal concerns. Many atheists find that delusional as well. I don't, as it's harmless, but, some do.
Is it delusional to sit in front of the religion channel, (which is basically the home shopping channel for the spiritually bereft) writing checks to a man in a bad hairhat who, waving spiritual baubles in your face, tells you you'll be "planting seeds in heaven"? Most atheists would say, yes it is. And sad, too. Yet millions give for "the harvest", and millions watch... rapt.
Is it delusional to hope the earth crashes and burns as soon as possible, so the "righteous" will have their orgasmic epiphany as God raptures them? Yes, and most atheists find that idea abhorrent. Yet those people are out there.
Is it delusional to support Hagee the Obese when he proclaims that Bush is the Messiah and that Hitler was God's Great Hunter? Yes, most atheists would say so. Yet, the man has a large following.
That's why it is also great that a handful of people, like those above, and those who composed that new Manifesto, come along and try to bring people better role models... as well as to promote education and learning rather than feed into peoples' weaknesses.