Scribbler1 said:
But, the claim that murder=wrong is unprovable. We say it is wrong because of our instincts.
Instincts drive male lions to murder the cubs of other males. Is it morally wrong when they do this? Personally, I find it disturbing - however, I am not sure how to prove it is morally wrong.
I believe you start with murder=wrong as one of your premises. But if you stop to look inside yourself, and ask why it is wrong, you will find yourself saying things like "it just is" - "I just feel it is bad" - things like that. That is what happens when we come up against instinct - we feel a certain way without really directly understanding why we feel that way. Try asking yourself why you don't like pain, it has the same result.
Any ethical belief, if you ask enough questions, you can trace it back to instinct. For example, you mentioned religion. Religions teach a variety of ethics - but why do people who believe in that religion choose to follow those ethics? Christianity teaches people to obey for a reward, and that if they disobey they will face torture. So, they obey to feel good and to avoid feeling bad. But - why do they want to feel good, and avoid feeling bad? This is a legitimate question, but not an easy one to answer, except to say that it is a part of our nature. Why is it a part of our nature - an instinct? Evolution, God, both?
When I ask, why is infanticide wrong, it is a legitimate question. Clearly, infanticide is a subset of murder, but we find it wrong because that is the way we are. Can anyone prove that the way we are is right? Are lions who murder cubs right?
No one can prove the rightness or wrongness of abortion, because they cannot prove the truth of their starting premises.