Good luck testing one of the currently accepted "ethical system"-type religious beliefs.
The only kind of outcome of such a test that is "allowed" is full agreement with the ethical system. A lot of these systems are just as self-reinforcing and barely based in reality as Christian apologetics of Aquinas or Chesterton. The people holding these beliefs know this on some subconscious level and will viciously attack anyone who disagrees. It is only over time with many such "attacks" that a mass belief will die and be replaced by another one.
In fact, every one of these "ethical" religious beliefs came about the same way: it defeated another commonly agreed upon dogma.
This mechanism by the way is what runs civilization. One meme fighting another.
Git forks and merges still share a common ancestral history and are basically an evolution of the same idea. This is true of a real Git repo (it's one software project after all) and the kind of churches you are likely talking about (it's all just a theist religion after all). Christianity is a branch in the same repo as the ancient Roman gods. The Saturnalia feature is even there still :)
I was thinking more about ideas like: - can people be property? - is it a good thing to kill "infidels"? - can women vote? - can a 10 year old get married?
These are "religious" questions because there is no objective truth to the answer either way. It's all based on beliefs and consensus.
Before you downvote me into oblivion: the answers to all of these have historically been different than they are today. People in both times (past and present) would attack you if you disagreed with the status quo (there was even a certain civil war fought about the people=property one). I am not actually disagreeing with the status quo on any of the above.
However, it would be naive to think that we do not presently collectively believe some things that would be appalling to a future human. A good heuristic for these is: would I get attacked or mocked for questioning this?
See also: http://www.paulgraham.com/say.html
For me, it always felt like the interpretation of the Holy Books are changing through time as we understand science more and more. And it feels ironic to me.
Surely all christians today believe that tricking somebody with dubious pretexts into debt-based slavery (as often happens with human trafficking of sex workers, where women have to formally pay up their debts and incurring the costs that they captors incur in hosting them in sub-human conditions).
Um, no, it isn't. It's how Genesis was interpreted by most people of the Jewish and Christian religions throughout most of the time since it was written. What is a fairly recent phenomenon is people of those religions not interpreting Genesis (and the Bible in general) literally.
It's somewhat orthogonal to your argument, but I'd doubt that most people in "Christian countries" (which is a heterodox notion) are/were Christians. Mostly people in the past seem to have followed a societal model, largely imposed as a firm of control.
Where I grew up in the UK the village vicar was not a Christian according to most definitions (they didn't believe in central tenets of the faith as espoused in all the main creeds).
Catholicism has a lot of things that are contradictory to biblical Christianity from basic things like having "special" people, to indulgences which are so contradictory to biblical teachings the only possibly way they were accepted is because most people were ignorant to Scripture. And of course those in power keenly maintained that ignorance.
The powerful hoping to keep people ignorant seems like conspiracy/folklore.
That's only true if you consider the Bible as the only source of revelation, which is not the case for Catholics, where Tradition is equally important.
Catholicism still has things that are contradictory to biblical Christianity, such as priesthood of all believers, even if you accept other sources of revelation those sources would still be contradictory.
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.