The fact that most people in a given civilization were Christians does not mean that the particular religious beliefs I was talking about were the ones that kept the civilization together. In fact, as the example I gave of religious wars over "homoousios" vs. "homoiousios" illustrates, those particular beliefs often caused problems that created huge rifts in the civilization.
> someone who has no idea how to keep any society together
If you are referring to me, I have no idea what you are talking about.
> Not only does the work of Aquinas have value
I guess we'll just have to agree to disagree about that, at least as far as the particular beliefs I was referring to are concerned, since that's the particular work of Aquinas that I was discussing.
> no ethical system that we hold dear has a chance of keeping anything going for even three generations, let alone 100
Ethical systems are not the same as the kinds of religious beliefs I was talking about. Ethical systems have practical consequences that can be tested. I agree with you that many people today appear to have ethical systems that don't work well; we know that because they have bad practical consequences.
However, when you talk about keeping things going for 100 generations, we don't have any single ethical system that has done that. Ethical systems have changed many times over the course of human history.