This is not true. Proof of the long-term optimality and utility of Golden Rule behavior in social animals. Proof of this is in the mathematics of game theory, specifically, the "Iterated Prisoners Dilemma". Over the long-term societies that practice this behavior will be wealthier and better off in general. There is nothing mystical about it; morons who don't play nice are removed from the gene pool just a little bit faster than those that do.
The real world is, of course, one long game of Iterated Prisoners' Dilemma. The more I think about it, the more it seems like the civilized world has been on a long term quest to find better & better refinements on the basic "tit-for-tat" strategy. Just for one example: The modern credit system would never work if we weren't able to track & easily publicize each borrower's reputation (their credit history) before each transaction. Meanwhile the "customer is always right" ideal, that is generally followed throughout the American retail market, can be seen as a variation of the forgiveness bias rule which, when added onto simple tit-for-tat, stops feuds from going on forever. Etc.