Does naturalism better explain the fact of ethical disagreement in the world better than theism does?
There can be no doubt that there is much disagreement when it comes to ethics. When it comes to normative ethics and meta-ethics, ethicists disagree on a lot of things (i.e. moral realism, divine command theory, utilitarianism, virtue ethics, etc). And when it comes to applied ethics, ethicists and laymen alike disagree on a number of things (war, death penalty, euthanasia, lying, etc.).
On theism, it is surprising that there exists such ethical disagreement. Why? Because God (if God exists) wants us to be able to do what is morally right. The theist believes that God wants us to do the right thing, but the theist also believes that God has left us in the dark about what the right answers are to certain ethical questions.
However, on naturalism, there is no God. Just nature that is impersonal, so that gives us good reason to expect less ethical agreement.
Note what I am not saying:
1. I am not saying that moral facts don’t exist
2. I am not saying that some moral facts don’t count as evidence for God (not claiming they do either)
3. I am not saying ethical disagreement means moral facts don’t exist
4. I am not saying there aren’t a lot of ethical issues that we do agree on