It is difficult to convey exactly how charismatic, convincing, and generally smooth the Geiers are. I've been trying to put the matter to words, and failing repeatedly. I have deleted the text of this message several times and started over just as many.
I suppose one anecdote from meeting them -- while minor -- will help. I knew several of the parents there. One of them was a highly qualified clinician who I've had a degree of experience with. She has always been among the more reasonable of the professionals in the area (in certain respects, anyway -- I've never worked with her clinically) and is a highly intelligent speech-language pathologist with a nineteen-year-old autistic son.
Said son apparently showed an interest in pornography for the first time rather recently. After attending the Geiers' presentation, she is now looking into getting him chemically castrated.