That ‘tit for tat’ you speak of is the Golden Rule; and while that
is, in fact, the basis of an absolute moral code (murder is
absolutely wrong because I don’t want to be murdered), the issue is a separate one: that it is not
objective.
Objectivity is, of course, generally something to be valued; and it is true that, say, the Categorical Imperative possesses that quality in lesser degree than does ‘natural law’. However, ‘natural law’ achieves that objectivity by sacrificing maturity. In the end, the Categorical Imperative says ‘act like this because you want everybody to act like this’; ‘natural law’ says ‘act like this because Daddy said so’. It’s a childish morality, one based not on thought and reason but on fear, subservience, and an arrogant presumption that one is already in the Right.
But how objective is ‘natural law’, anyway? Ask three different people what mores it enforces and you’ll get three different answers – at least! And each answer will come with myriad assurances of its rectitude, and usually with a footnote that the respondent is a shining example of how to live a Moral Life. Interpretation of ‘natural law’, then, pretty much depends on the person – making it about as objective as one’s favorite color. Or, if you like, as objective as the Golden Rule. The Categorical Imperative actually has a leg up on it with the concept of universalization.
Sure, the intentions are irrelevant – intentions don’t affect anyone else. Actions do. As for relevance, you’re pushing the human ego just a little there. ‘ACKNOWLEDGE ME, UNIVERSE!’ shouts the gnat.
Ozymandias’ statue ended up buried in the sand, with its inscription ‘Look on my works, ye mighty, and despair’; what makes you think you’re any more special than he?
I gave an answer in the first reply to the thread
Maybe you haven’t spoken with many nontheists who’ve given this particular matter a good deal of thought; ah well, plenty of believers don’t care enough to think it over either.
Thanks