If human good is not merely a matter of opinion in every case then #SituationalEthics is the best description of the world. So, that is what you have to consider before you accept that all good is a matter of opinion (i.e. moral nihilism). People reject natural rights as though that is the best case for natural goodness.
I make some arguments for #SituationalEthics in my featured writing Classical Philosophy > Classical Liberalism.