Codifying Ethics

I was reading my ethics textbook and it was talking a little bit about whether or not religion is relevant to ethics. It notes that many philosophers and theologians have considered morality to be entirely dependent on religion, gods and the like. But I was thinking on it and came to the conclusion that it's more likely the other way around. Here's my reasoning:

1) If religion is the basis of morality, atheists would have no morals
2) I am a moral atheist
3) Therefore religion is not the basis of morality

Note that religion may be the basis of some people's morality, but not morality in general. So what is the relationship between morality, ethics and religion? In my opinion, it's rather that religion is the codified version of the natural moral urges inherent in most humans. But something gets lost in translation. Why is it that so many moral codes are so removed from human nature? Other than the golden rule (which has it's own flaws) many moral codes seem to be adverse to pleasure and reason. One theory I have is the notion of the corrupting influence of power. Another could be the sociopathic tendencies of the mentally ill people who often became shamans and prophets in the ancient world.

Whatever the reason, it seems that morals are much better off as a natural phenomenon of the human mind than a codified religious law.

Codifying Ethics