Morality is collective; we coordinate together to define and then enforce shared morals. Due to rising wealth and an explosion of fiction, the modern world is way into morality; even when other needs are sated, we still crave self-righteousness. The modern world has also greatly raised the status of education, and thus of abstraction. Combining these two, the modern world is very into abstracting morality; we celebrate intellectual systems that try to organize how we think about our moral choices.
Oddly, however, we have four different spheres of life where we make collective choices about morality: religion, politics, law, and personal behavior. And each of these spheres has quite different associated organizing abstract intellectual systems:
We organize our opinions on religion via religious epistemologies, such as traditionalism, scripturalism, rationalism, and mysticism.
We organize our opinions on politics via political ideologies, such as liberalism, conservatism, socialism, and libertarianism.
We organize our opinions on law via legal philosophies, such as natural law, realism, positivism, interpretivism, and law & economics.
And we organize our opinions on personal behavior norms via ethical systems, such as utilitarianism, deontology, virtue ethics, and care ethics.
These are very different sets of abstract intellectual systems for roughly the same task, organizing our opinions on moral choices. This seems to me to call into question their generality. We should expect truly general moral frameworks to organize our moral choices well in all of these areas. This seems to be an argument for the usual economists’ approach to policy advice, which does in fact use pretty similar tools and standards to advise choices in diverse areas.
Re politics, I know that preferences and choices re specific government policies are at best only weakly correlated with abstract political ideologies. I presume the same is true also for religion, law, and personal norms; choices of abstract systems correlates only weakly with specific choices there. This suggests that such abstract systems function more to show off intellectual abilities, and to create and manage groups and coalitions, and less to advise more particular choices of policies and behaviors.
In the first three of these areas, religion, politics, and law, we usually recognize that, to be feasible, intended behaviors must be accompanying by sufficient monitoring and enforcement to make it usually be in the selfish interest of individuals to conform to those intentions. God can see and punish all, and we usually limit our choices of government and legal policies to the promotion of behaviors where sufficient monitoring and enforcement can be recruited to achieve desired results.
In contrast, many often exhort people to follow the personal behavior recommendations of ethical systems even when they don’t expect sufficient monitoring and enforcement to make such actions be in an individual’s selfish interest. Yet habits of taking actions that go against one’s adaptive interests should be selected against by DNA and cultural evolution. Which should then select against the habit of listening to people who advise such tendencies.
This seems a mistake. The people who reason abstractly about religion, politics, and law get this; why can’t those who reason abstractly about ethical systems? Thus ethical systems should limit themselves to recommending behaviors for which sufficient monitoring and enforcement can be recruited to make them be in individuals’ selfish adaptive interest.
"why can’t those who reason abstractly about ethical systems?"
Because humans are terrible at philosophy, basically. Ethicists mainly concern themselves with metaphysical nonsense that has almost nothing to do with moral questions that real people actually face, and actual morality that societies operate under is almost entirely tacit and unstudied.
You say: "ethical systems should limit themselves to recommending behaviors for which sufficient monitoring and enforcement can be recruited to make them be in individuals’ selfish adaptive interest."
Two things about this. First, many ethical systems are about going beyond selfish adaptive interest. So saying they should limit themselves to that, is in itself a choice among ethical systems.
It's also an is/ought fallacy. As humans we are free to chose moral systems that go beyond self-interest. Just because evolution works a certain way doesn't commit us to anything.
I'm also not sure I agree with the tightness of the categorization. Morality surrounding religion is also strongly about how to organize our personal lives and to some degree about how to organize our politics. Morality surrounding politics is also about how we should organize our personal lives (e.g. liberalism commits us to tolerance on a personal level too. etc.) The intellectual systems are distinct like you say, but the practical consequences of these systems bleed into each other strongly. So it's questionable how really separate they are in practice. E.g. we can reject a political system based on religious or personal morality or a system of law based on our religious convictions.