That simple thought experiment incentivizes bad actions from time to time.
The optimal strategy, in theory and practice, for the iterated prisoner's dilemma (unknown or infinite amounts of iterations) is some version of tit for tat, details depending on the exact rules (such as low information reliability needing increased forgiveness). The strategy involves punishing the other player for defecting but it will never defect first so two tit-for-tat players will play 100% cooperatively and the knives stay where they belong, behind their backs. Holistically speaking choosing to punish is not bad because it incentivise the other player to play cooperatively, leading to overall greater results for both.
Evolutionarily speaking: If cooperation did not give advantages, why the fuck did we become a social species? Going for anti-cooperative strategies only ever makes sense in zero-sum games and practically nothing in life is.
You have more to gain by acting selfishly.
That's capitalist propaganda with no basis in game theory.
Not every choice is a conscious decision in my eyes, but the vast majority are.
Oh my sweet summer child.
Then being nasty wins out, no matter the length of the game as long as it's known (or at least an upper bound is known) But that's not the case in practice so it's irrelevant which is why I specified (yes I mentioned it) infinite or unknown amount of iterations.
That mark. That thing we consider good. The innate sense, what pretty much everyone agrees on. It is there because our ancestors were successful because all that game theory stuff happens to apply. If it didn't, then we would consider defecting good, not, to sum it up neatly, "never start a fight but always end it".