>. But "a sound fundamental philosophical justification" doesn't appear to have any meanin

You're saying the entirety of moral philosophy has no meaning so people should just do whatever they feels like, that's a pretty barbaric position.

>So I default to appeals to utility

Utility also relies on a philosophical justification; if you throw out all philosophy, you also throw out utilitarianism.

https://en.wikipedia.org/wiki/Natural_rights_and_legal_right...