Because there are lots of stupid people around them that make life miserable for everybody, not only themselves ! Note: I wrote this comment after reading just the title...
You should definitely read the article, it's pretty good. That said, I'd say it's not the stupid that make life miserable for everyone else, it's the smart people that were born earlier. A smart person with power sets rules to benefit themselves. They may or may not care about what happens after they die. Those that care will almost certainly want to advantage their descendants and friends. Enough iterations on this same pattern and you get the kafkaesque and at times idiotic modern society.
I disagree, I think it's more about a person's emotion intelligence. You can choose to be happy even if everyone else around you is not. It might not be easy, but I think it's possible.
Totally agree. One might require to be "in their head" a lot of the time to not get swung down, and enjoy himself such as laughing at his own jokes. To make it possible, one has to be free enough to express oneself (also internally). But freedom of thought and action is on the decline as I've come to observe lately, but that's another topic.
