Please note that the post gives an extremely bad impression. First of all, pareto efficiency and nash equilibria exist both in capitalism and other economic systems. And the obvious alternative economic system : centrally planned economies, are very much nash equilibria (if they are stable at all).

But the second impression he gives is also very wrong. By definition, everyone is a "selfish dickhead" both in Nash equilibria interactions and pareto efficient interactions. This is a basic tenet of economy, that people "in the limit" act in their own self interest, never out of altruism. Why ? Simple : if anyone is systematically altruistic, he/she will be eliminated from the game (meaning end up dirt poor, imprisoned or dead or otherwise prevented from participating in the system). The predictions this makes are extremely accurate, and have been for millenia.

Always assume nobody is altruistic, ever, for any reason.

The real difference between nash equilibrium transactions and pareto efficient transactions is this :

nash equilibrium : A and B, both "selfish dickheads", transact. If A gets a good deal, B got screwed.

Pareto efficiency : A and B, both "selfish dickheads", transact. A and B got a good deal.

This is why the "always cooperate" strategy in the prisoner's dilemma game is not actually pareto efficient : it is obviously possible for the other guy to screw you. If it were a pareto efficient strategy, it wouldn't be possible to take advantage of this.

In capitalism, if there is a pareto-efficient strategy to transact, people following that tactic will quickly increase in numbers, and therefore the whole society will become pareto efficient. This happens BECAUSE everyone is a "selfish dickhead", not because some people are morally superior to others. That fact is why every economist is so impressed with capitalism. Capitalism is a system that can succeed, for everyone, in the presence of selfish dickheads. A centrally planned economy, by contrast, necessarily either destabilizes entirely (not good for anyone, unless you truly believe in anarchism), or turns into a Nash equilibrium over time.

Capitalism is a learning algorithm, or a "crowd-sourcing" algorithm with money as "karma" : it makes sure that resource allocations are decided by people who previously made good allocations. That is of course what people really have against capitalism :

1) "abusers"/"power mongers"/... : complain about capitalism because they can't keep abusing the system. If they use their resources to force certain outcomes that wouldn't normally be achieved (e.g. personal power), that can only work for so long.

2) moralists: complain about capitalism because it's amoral, like any learning algorithm. It does not care if any action improves or destroys other people, or which factors determine success, merely if it increases an abstract "value" concept. If they have resources (e.g. because you have an islamist state), it requires a constant large cost to force any non-optimal outcome (e.g. not letting women work). Needless to say this is perceived by the moralists as capitalism fighting allah (when of course it's really reality itself that's at odds with allah), and then they usually just grab the weapons.

If there ever was a "true" religion, it's trivial to see capitalism would quickly grow it, not work against it. "Surprisingly" this has not happened yet, one can only wonder why.