Is nihilism the logical extreme of atheism?

[genkaus]

Perhaps. However, if God's will is the ideal, the most perfect good possible, the locus of meaning, the essence of value, the purpose of purpose, per se, then...?

Even if it is all that and more, all those things are still subject to god's will and therefore subjective by definition.

I think it basically boils down to whether or not any ideal is properly considered objective or not.

Depends upon the ideal and on what basis it is considered so.

If we can agree that certain ideals are binding in some way, through some logical necessity or what have you, then the theist could just substitute God for the ideal, and avoid your nihilism, could they not?

That is what theists often do - and that is what results in self-contradictory and illogical nature of their god.

I'm not sure I quite understand the rationale in how a "a universal moral law inherent and intrinsic to human nature and one that provides your life with objective purpose, meaning" can follow where the existence of such laws are only defined by individuals in a particular species (values, as in morality I think, requiring separate consideration, where the universal moral law seems tantamount to the ideal).

It doesn't have to be defined by individuals in a particular species - the law would be applicable to all entities capable of rational consideration. It just so happens that humans are the only known species capable of it.

The rationale here is that the universal moral law can only apply to beings capable of moral action - that is, rational beings - and values, purpose and meaning derived from it would be objective because the law does not depend on any one's will or desire but is tantamount to a fact of nature.