Civilization must suppress humans' natural sexual and aggressive desires to enable cooperation at scale. This suppression of desires naturally leads to increased discontent. Freud suggests that all civilizations may inherently create more psychological suffering for individuals due to this effect.
An insightful idea but Freud's justification here is lacking. I expected him to focus on the suppression of primal desires to prevent violence. Instead, he suggests that the existence of social norms and morals causes individuals to suffer more as they feel guilty about their true desires. This is a far less compelling argument.
This book also feels more like Freud thinking out loud rather than him presenting an argument that has already been fully synthesized. In general, I find that his psychological theories tend more toward opinionated narratives, rather than beautifully synthesized fundamentals that are empirically justified.