I think that you are referring to Scientology, seeing as his father was the highest ranking Clam Worshipper in Europe until his death, and Mr. Gaiman's sister is in the cult and his ex-wife is a believer? I had a similar reaction, but he has publicly denied any involvement with Scientology (anymore), in an interview with the BBC in 2010 iirc, so I have relented. I suppose he could have been lying, but I choose to believe that he wasn't :-)

Having said all of that, totally respect you taking a stand on it; The Church f Scientology is a hateful organisation.