I wasnt objecting to utilitarianism.

I know, my point referred to people using "ethics is from humans for humans" in a way that would also rule out transhumanism.

Belief isnt the important criterion. The important criterion is whether person B can argue for or against what person A takes as automatic. How do you show objectively that claim can't be argued for, and has to be assumed.

The burden of proof is elsewhere, how do you overcome the is-ought distinction when you try to justify/argue for a claim? Edit: To repraphse this (don't know how this could get me downvotes, but I'm trying to make this more clear), if the arguments for the is-ought distinction, which seem totally sound, are correct, it is unclear how you could argue for person A's moral assumptions being incorrect, at least in cases where these assumptions are non-contradicting and not based on confused metaphysics.