I'm not saying it's not possible to find other equilibrium points. I'm just pointing out that there are more fundamental forces at play and it's not just becaus

I'm not saying it's not possible to find other equilibrium points. I'm just pointing out that there are more fundamental forces at play and it's not just because of our "monkey/animal brain". Selective pressures that permit the emergence of cooperative behaviour require participating individuals to exhibit a variation in behaviour and those who cooperate result in having a higher fitness in the environment than those who shun cooperation. The selection effect operates on over the whole population and over times that are longer than the life span of an individual. An individual that is implementing what ultimately will emerge as the winning strategy, may on average be better off, but it can (and it will) be also often worse off. Depending whose existence you're optimizing for (individual or species) changes the framing of what is the optimal strategy. An existential risk for a species changes the framing of what is rational to do quite a lot.