I have an interesting thought concerning morality and I would like to see what other people's thoughts are. It seems to me that at the core of it morality is simply distinguishing between behaviors that are acceptable or not acceptable and it seems like pretty much everyone would agree with that definition and it wouldn't be very contentious. The concept of morality developed because it is necessary to distinguish between acceptable behaviors and unacceptable behaviors for us to function cohesively in society and survive together.
What seems to get debatable and more contentious is what the framework for moral decision-making or distinguishing between acceptable or unacceptable behaviors should be. Should it be religion? Should it be culture? Should it be tradition? One of my beefs with religion is that it gives people a framework for moral decision-making that is based on false information and it ends up causing unnecessary pain and suffering, like if people are starving to death in another country because it is believed that cows are sacred and cannot be killed and eaten. Or a Christians framework for moral decision-making might be if God says it's right it's right and if God says it's wrong it's wrong and that is how they distinguish between acceptable or unacceptable behaviors and it's obvious how that can unnecessarily hurt groups of people.
Personally I choose to use the well-being of conscious creatures as the framework for my moral decision-making because I care about the pain and suffering of others.
I would agree with your thoughts on the purpose of ethics. As far as looking to culture versus religion, I don't think that is exactly what is going on. There are many different ethical philosophies that have been debated since the times of the ancient Greeks. I think that religion generally follows Kantian ethics, but there are many other ethical philosophies with equal or better merit. (Photo source [medium.com]
I would certainly vote for culture over religion as the basis for what is and isn't acceptable. That's the point: Our culture has progressed significantly in recognizing the level of respect that should be afforded to those that are different. Religion mostly does the opposite, teaching to fear the other, and that outsiders must either be converted or shunned.
Religious morality is still mostly a reflection of pre-Technology Europeans with acceptance of slavery and cruel patriarchy as standard. Religious morality mostly lags cultural morality by at least a couple of centuries. Holding to cruel and simplistic values of religion is now understood as degenerate and indicates underlying psychopathy.