It is not really obvious to me that happiness should be part of the social contract.
Happiness is very slippery even in your own life. It seems absurd to me that you should care about my happiness.
So much of happiness is the change from the previous state to the present. I am happy right now because 2026 has started off great for me while 2025 was a bad year.
I would imagine there was never a happier American society than the year's after WW2.
I imagine some of the most happy human societies were the ones during the years after the black plague. No one though today gains happiness because of the absence of black plague.
To believe a society can be built around happiness seems completely delusional to me.