Is "Natural Law" sufficient?

[This post can be found at the new site, here]

In the argument over homosexuality, people have argued to me that, since the act can be found in nature, it must be a natural thing. I think this argument is primarily a response to the argument I have heard many Christians make: Homosexuality is "not natural", therefore it must be immoral.

However, both of these arguments are essentially arguing for the same point: What is found in nature is the foundation for morality. The pro-homosexuality side says "because it was found in nature, therefore it is morally acceptable", while the anti-homosexuality side says "Because it was not found in nature, therefore it is not morally acceptable."

But the implied argument, often unrealized, from the anti side is that if it were found in nature, it would be morally acceptable. Of course, both sides of the party are in a veritable pickle: If all things found in nature were somehow morally justifiable, such things as murder and non-consensual sex would be also morally justifiable, since they are found quite commonly in nature.

If we, as Christians or non-Christians, use nature as our guide for what is moral or immoral, neither of us will have any ground to stand on when we discuss homosexuality or any other action. To be fully consistent, all of us must argue from a foundation of where our authority comes from to be able to call something moral or immoral, right or wrong.

For a non-Christian, that authority comes from another religion or from an implied social contract, but a Christian must argue from the fundamental authority of God's revealed Word, the Bible. I believe this is true whether we speak of general abstract morality, or specific actions being acceptable, or political views being reasonable.