"Happy families are all alike; every unhappy family is unhappy in its own way"

This, to me, is clearly false, and citing an aphorism in a work of fiction isn't particularly strong evidence for it. What I do believe is that, at any given moment, there are fewer moral courses of action than immoral courses of action, but that does not mean that in a given culture, of the realm of immoral actions available (in theory), the number used is much higher than the available number of moral actions. This is because people tend to defect from morality in similar ways. For example, not committing adultery has a fairly standard method of defection.

Really, I disagree with Scott's entire premise of defining morality purely in terms of cooperation. Why solely cooperation? What Scott is missing is that a moral system has to actually be viable across generations as well. That's easy for him to do with a model of infinitely lived agents, but harder to do in a model of finite lived agents where each generation has to "teach" the code to the next, and younger generations can choose to change the rule of the game.

For me, morality can only be observed in relation to adhering to a code of behavior, and then you need to define the morality of the code itself to get the actual morality of the behavior. Moreover, the morality of a code only makes sense in a relative context (is one code better than another code or than a group of competing codes). In my opinion, the best neutral definition of success is greater reproductive success, where by "reproductive", I mean social reproduction. So a moral system that reproduces itself across generations more successfully than another is more moral. This requires 1) that people within the group continue to believe in it across generations, and 2) the group that believes in it grows and thrives across generations.

Especially in a hostile world where there are rival groups and rival moral systems waiting to dismantle your group and your system, and there are many opportunities for decay from within as well. That code is supposed to light your way through these treacherous rocks, so that your society will survive the challenges it faces.

For example, communism won over large parts of Eurasia, but within a few generations people stopped believing in it and abandoned it. So it was not a very moral system. A more moral system would be one that survives for thousands of years, successfully reproducing in each generation and ensuring the reproductive success of those societies who practice it. Thus fundamentalist Islam would be a more moral system than communism. Whether fundamentalist Islam is more moral than liberal Western Democratic norms remains to be seen -- who will outlast whom?

And I think if you go back to traditional moral codes, they were explicitly designed with the threat or promise of reproductive success if the code was followed. E.g. from Deuteronomy 30:16-19

"In that I command thee this day to love the LORD thy God, to walk in his ways, and to keep his commandments and his statutes and his judgments, that thou mayest live and multiply: and the LORD thy God shall bless thee in the land whither thou goest to possess it. But if thine heart turn away, so that thou wilt not hear, but shalt be drawn away, and worship other gods, and serve them; I denounce unto you this day, that ye shall surely perish, and that ye shall not prolong your days upon the land, whither thou passest over Jordan to go to possess it. I call heaven and earth to record this day against you, that I have set before you life and death, blessing and cursing: therefore choose life, that both thou and thy seed may live"

So on a long enough time scale, might makes right, or morality is judged by the success of the people who adhere to it. If you follow this code, you will be stronger across many generations than a rival who follows a different code. That makes your moral code more correct. This is hinted at in suggestions like Tit-for-tat being more successful of a strategy, but then there is a lot of extraneous talk about "cooperation", when societies that explicitly orient themselves on the basis of maximizing cooperation end up collapsing after a few generations, or remain completely stunted and are wiped out by more robust societies that do not solely focus on cooperation. You can see Scott struggling with this in his eigenMoses or eigenJesus choice, but really that is the first of many stumblingblocks he would face if he had more agents interacting beyond the model of a repeated game.