What is the difference between:
1. tells you what you should do
2. points out what an optimal course of action is
From which are we better off drawing our conclusions?
I'm guessing you favour the second option.
But 'should' and 'optimal' are cut from the exact same cloth: subjective judgement
Illustration: 'Optimal' under whose interpretation? What is optimal for the deer is not going to be optimal for the lion. Optimal just collapses into Should.
More generally, I cannot see what a 'deductive value system' is. It sounds to me as though 'deductive' is being used to impart some sort of objectivity to some limited class of value judgements: those that are 'optimal', what ever that means.
Nihilism means that NO value judgements, of any sort, follow logically (deductively) from the mind-independent world. This doesn't mean nihilism has no function (personal or subjective), it's just that its philosophical
, or objective, function is purely negative.