What Bill said. I can't speak for him, but my local chapter is excellent evidence of why they have their own club. They're seriously unable to adapt to the world most of us live in. I have a feeling that people who are really into Mensa are people who have high IQ scores, and have difficulty in the real world. Most high-IQ people work in fields where they meet lots of other high-IQ people without any need to go to Mensa meetings
Last I heard, Mensa thought Hitler had the right idea but just went about it the wrong way.