That's obviously not true. Is it ethical to have slaves or kill children? No, objectively, it is not.
You are objectively using objectively wrong :-P (sorry, couldn't resist)
Disclaimer: I agree that having slaves or killing children is very wrong.
Ethics are an objective analysis framework. Morals are subjective.
There are plenty of ethical frameworks where those examples you give objectively evaluate to βyesβ.
That's obviously not true. Is it ethical to have slaves or kill children? No, objectively, it is not.