[HumanaeVitae]

What you're talking about is the "No True Scotsman" fallacy...in other words, if a Scotsman does something that isn't in accord with true Scotsman-ness, then he isn't a Scotsman and thus not truly representing Scotsmen, right?

I think we're arguing around each other, so I'm going to try to nail down exactly what you are trying to prove here.

I'm attempting to show that ethics are non-derivable from empirical facts, and thus the claim of 'objective ethics' is flawed. Please elaborate.

[ThinkDifferent]

I think we're arguing around each other

Agreed.

I'm attempting to show that ethics are non-derivable from empirical facts

My claim is that regardless of the source of ethics, there must be a rational way to decide among multiple incompatible ethical systems. Otherwise you can't condemn anyone's actions if they have a sincere belief that God supports them.