The thing about capitalism, and our dismal history with capitalism-at-large, the “assume the other party is a shitbag” idea is so fundamentally ingrained in our cultural DNA that it is very hard to imagine any other form of collaboration/competition where this assumption doesn’t hold. There’s an argument to be made that when capitalism is local, IE, you can look the other person in the eye, you both know each other, and the village will hold you accountable for your actions, this contstraint can be relaxed somewhat. And indeed, research into an iterated from of the Prisoner’s Dilemma — having players play multiple rounds of PD, as opposed to a one-shot game — appears to bear this out somewhat.
I believe our unfortunate heritage with capitalism, and our steadily decreasing trust in other Americans, is exactly how we end up with these intractable tragedy of the commons-type situations, where no individual party is willing to be vulnerable enough to move toward cooperative solutions in lieu of safe, selfish solutions. The longer this cultural feedback loop persists, the harder it becomes for any one party to make any meaningful move toward a Pareto optimal solution without inviting an equal-but-opposite increase in skepticism toward the first mover. And it’s been persisting in this direction for quite some time. This explains, at the very least, why rampant partisanship is an inevitability in a large Democracy, despite it being worse off for everybody (including politicians themselves).