As a member of Mensa, I found to my surprise that people looked down on it with a certain vigor. Elitist, snobby implications perhaps, or a friend used to say, "You aced the Mencap test!", much to his amusement! (Mencap is an association for the learning disabled in the UK.)
To me, it is nothing more than a) finding out where I sit on the continuum of intelligence, b) a place where you can meet like-minded eggheads. I see this as no different to any group where people have a common interest. Perhaps it stems from a deep-rooted inferiority complex.
Anyone else here experienced reverse mental snobbery?