JohnStuartMill wrote:To say that something has no rational basis is to say that it has NO basis.
If morality has no rational basis, then how could you prefer one system over another? You'd have no reason to do so. You might as well say "arf darf kablooey chargey-margey rammalamma ding-dong, therefore we must fight Mormonism to the death".
Contrary to your nihilistic viewpoint, morality DOES have a rational basis. What this basis is is disputed (although I myself believe that the question is pretty much settled in utilitarianism's favor), but it's possible -- indeed preferable -- to believe in a binding morality without introducing supernatural elements.
http://fair-use.org/john-stuart-mill/ut ... hapter-iii
Morality is always based on some preconceptions that can't be explained rationally. When you get into more complex situations then yes, rationality is used to adjudicate between two moral stances.
For example, killing is wrong is one preconception. Another could be that we owe a sense of duty to our tribe/nation. Another could be that we have a right to self-defense. Okay, now someone is considering joining the armed forces of their nation at war. They have to rationalize between the moral stances to determine which is more important and which has priority in this situation. This is why from the same moral base people can be pacifists and non-pacifists. There is room for rationality there.
However, when you get down to base principles such as:
"The Human race should survive."
"I must protect my children."
"I must defend my people."
there is no way to rationalize them except to argue that they are instincts. If they are just instincts why should I be bothered to follow them? Why should I want the human race (or even myself to survive)? Why do I owe my children protection? Why do I owe my people anything at all? I can't answer these questions except to say that I want the human race to survive, will protect my children, and will defend my people because I consider it to be right.
"Surely he knows that DCP, The Nehor, Lamanite, and other key apologists..." -Scratch clarifying my status in apologetics
"I admit it; I'm a petty, petty man." -Some Schmo