people are painted as too stupid, selfish, and vengeful to actually build something new out of the ashes

Idk about that. The various factions are fighting over limited resources in the midst of a deadly pandemic and - what functionally amounts to - an endless guerrilla war against zombie-monsters.

We’re seeing instances of civilization persisting (eps 1, 2, 7) in a dystopian state, instances of civilization collapsing (eps 3, 4, 5, and 8), and instances of it thriving (6). But people aren’t portrayed as stupid or selfish so much as they’re portrayed as frightened and confused.

Whether its Fedra v Fireflies or the Christian Cannibals or the dynamic between Elle and Joel, there’s an underlying terror that runs through these relationships. People are terrified of the disease, they’re terrified of each other, they’re terrified of what happens when their supplies run out, and they’re terrified of dying for nothing.

Time and again, the decisions made by the characters is dictated by how they respond to their fears. And the drama is driven by conflict as characters diverge or collide in response to their fears.

Its easy to call individuals suffering from paranoia or depression or a deep-seated phobia as “stupid”. But so much of the show is intended to be empathetic towards these people - even the really horrible ones - by exposing and expounding on these fears.