>It seems odd that an absolute would depend on something subjective, doesn't it?
Go deep enough and eventually everything is subjective. Even things like fundamental axioms.
Explanations.
That there exists more than one explanation for a phenomenon, like ethics and moral values, doesn't mean that choosing any of those at random yields a good explanation. It also doesn't mean that there is no valid explanation at all.
That's just lazy not-100%-sure-therefore-I-substituite-my-own-reality-ism.
It seems odd that an absolute would depend on something subjective, doesn't it?
we would not be able to trust each other.
That sounds like a pretty utilitarian concern to me, rather than a contradiction.