Finally, I disagree with Kadczynski, but I think Kadczynski has a point. I think your analysis is too rational. So, when Kadczynski says “people in primitive societies are happier”, you reply by giving objective data (people lived shorter lives, there were more diseases, more work, worse sanitation, etc.). You also acknowledge the disadvantages of civilized society (too many rules, etc.). You make a rational analysis of pros and cons and conclude that modern life is not that bad. I wholeheartedly agree with this.
But your analysis only shows that people in the past lived worse lives than ours. Not that people weren’t happier back then. Because “living worse lives” is an objective measure, but happiness is something subjective.
I have lived in USA, in my country (Southern Europe) and I have lived for the last 20 years in Central America. When you compare countries, USA is the country with the best standard of living but where people are more miserable (and have a higher rate of use of antidepressants). The country I live now is the happiest one, despite being dirt poor and violent. Southern Europe is like USA but not that extreme (less rich, less miserable).
(I used to play a game when I lived in the US. When I walked, I counted the number of people I came across until I saw a person who had a “good” expression on his face -a expression of happiness, a expression of contentment or peace-. Sometimes the number was higher than 100).
How is this possible? It is because unhappiness is the difference between reality and expectations. People in rich countries have very high expectations that are often unfulfilled (see the riots). People in poorer countries are trained to have lower expectations so they are happy with less.
In addition, the abandonment of (popular) religion also adds to unhappiness. In the country I live, even if they are not particularly religious and don’t attend religious services, people are positive that God will help them and that everything will end up OK (sometimes against all evidence). This makes them endure the highest storms with more tranquility.
Finally, modern life is an artificial construct. The natural state of mankind is to be dirt poor (this natural state was 99% of the history of humanity). Therefore, in order to sustain a wealthy civilized society, you have to psychologically change the people so they fit in this artificial construct. People have to be more selfish and focus more on material things that in extended family, etc. This Theodore Dalrymple article explains it very well: https://www.city-journal.org/html/after-empire-12420.html
This makes them richer but more alienated. Their biological nature is wired for a poor primitive society and the behaviors adapted to this poor society. If you give your dog a life of leisure and wealth but you don’t allow him to bark and run, you will get an unhappy dog.
(I know that there is a rebuttal, “if they are so happy, why do they come here? why don’t they stay in their countries?” But the reasons for immigration are complex and this comment is already too long).