MENSA always struck me as an arrogant elitist society of people bragging to each other about how smart they are. There's a cruder term to describe what I think about MENSA, but it is not appropriate to use here on FR.
I'm pretty sure that my IQ far exceeds that needed to join MENSA. However, I'm not an arrogant elitist who needs to brag in order to feel good about myself.
I think your post answers the question posed in the thread title. As we FR folk gather because of many common interests so might people with other shared traits such as a high IQ.
Mentioning membership in such a group on your job resume is not advised.
A friend of mine is in Mensa and holds meetings in his house. I'm not a member, but I'm sometimes there hanging out.
Mensa appears to have a number of members who are not as successful in life as their IQs would indicate they should be, due to personality issues.
Think about it. Most really smart people are in professions where they interact all day with lots of equally-smart people. They don't need to join Mensa.
The original concept of Mensa was that smart people would get together and think of solutions to the big problems. The concept made some sense at first, before the age of technology. It gave people from various backgrounds an opportunity to get together and share ideas, philosophies, and thoughts. It quickly devolved into party central for nerds.
Then technology changed the dynamic. A physical group became less necessary and interest in abstract discussion declined.
There are still some dinners where Mensans get together for discussion and a thought-provoking speaker. I wouldn't paint all of Mensa with one brush. For people who dwell in the world of ideas, it's a really nice social outlet.
You just did.