[skissane]

You are assuming naturalism / physicalism / materialism is true.

I agree, that if naturalism / physicalism / materialism is true, then the concept of "objective good" becomes hard to justify. Certainly, some people have tried, but a lot of people question whether those attempts can be successful – indeed, doubting those efforts is one thing that both naturalists who doubt the objectivity of the good, and non-naturalists who believe in the objectivity of the good but reject the idea that it can be given a naturalist foundation, can agree on.