I would theorize that in the brain there are parameters that determine how likely and to what effect that they will remember and spread the idea. Then in general populations these parameters fit general trends. So any idea could fit these parameters but false ideas are more malleable to fit the parameters and thus increasing their spread.
For the third question, free-market capitalism might have fewer interactions between singular agents but more interactions between groups of agents. With the agents in free markets are still able to share information between each other changing it more into an iterated game. It does this while also increasing the punishment for defecting by having the group defect against the individual. Though the information sharing is not always consistent allowing for bad actors.