Regarding Mensa itself, or any claims to intellectual superiority: one of the big lessons of my life has been that being intelligent has no intrinsic value. If you are unable to manifest your intelligence in a way that can substantially (disproportionate to your effort) improve your life or the lives of others, then your mind doesn't matter. It has no impact in the world, and I am not the first person to observe that having a powerful mind is at many times a burden.
You can see that other people may be more stupid than you, forwarding simpler arguments and relying on less rigorous thinking than yours, but if they don't want to be convinced of that, then you are powerless to make them see it. They go off blissfully, and you burn with anguish. Again, if you cannot manifest your intelligence in a way that forwards your agenda, who cares?
To phrase it in a more confrontational way: if nobody is forced to contend with your mind, nobody knows it exists. Or to summarize it in a quote:
"[Intelligence] is like being a lady: if you have to tell people you are, you aren't." -- Margaret Thatcher
This clicked for me during my final year of college, when a friend of mine was taking an LSAT preparation course. During a break, he was chatting with the instructor about realistic outcomes, and said earnestly that he hoped to get a score of 168 (which IIRC is a very high score.) The instructor, a man of maybe 30, who had been out of school for several years, scoffed and replied, "Good luck, I only got 165 and I'm a genius."
And what did the genius do when not teaching LSAT prep courses? Why, he worked at Target.
Edit: expanded a little on the first couple of paragraphs.