You could make this type of criticism of literally any moral argument (swapping out utility for whatever the underlying criteria is in alternative moral frameworks). This is why post-modernist philosophy has become dominant in the modern world. There is no successful response to it other than to ignore it and and realize that it is all, "boring and arbitrary" as I said earlier.

Edit: Also, as I learned from a post-modern adjacent philosopher, Richard Rorty, there is sometimes benefit in making arguments in different moral frameworks even if you believe they are all ultimately arbitrary: different people are convinced by different lines of reasoning. But ultimately, I post on HN because it is fun.