Does that mean morals are largely subjective then? I'll never forget the interview with the Aryan Brotherhood prison gang member who said, "I've got morals, just not yours." Where's the line drawn?
Pretty much subjective, yes. There are plenty of societies that operate on way different moral standards than we do. The philosopher Sam Harris has given what I think is a good rule of thumb: "Imagine a situation worse than the worst hell you can think of. Everything is bad. Now you might be saying that there's a silver lining somewhere, but I wouldn't know what you'd be talking about. This called The Worst Possible Scenario For Everyone. Anything that moves away from that situation can be called 'right' and anything that moves towards that scenarion can be called 'wrong'.
The guy has written a book on this subject. It's called 'The Moral Landscape'. If you enjoy the subject of morality, this is probably a good book to start with.