Perhaps I wasn't clear enough. I didn't say a non religious moral system can't take harm into account, rather I was saying that a non religious moral system, can ONLY take harm into account. (Even thats debatable but I won't dispute it, not now at least).
I'm not sure that's actually true, but why would it be bad if it was?
Sexual relations among the closest family members for instance, if it didn't involve penetration (therefore with no risk of pregnancy), would be perfectly moral in a non religious moral system.
But you're ignoring what I said before about psychological and emotional harm. These could both happen in incest.
In addition to incest, the same goes with open relationships, lying when no harm is done (say making up stories to make people laugh), no one can say they cause harm. So if someone is willing to say all of these examples are moral, then fine, you have a non religious moral system. Not one that I accept, but it is a system.
So you have a different system; what's it based on and how do you know it's better?
Also, it seems like your objection to open relationships is a bit circular... either that or it comes down to "I find them distateful personally, therefore they're immoral for everyone."
But I don't think one can accept certain things like open relationships on the basis that they aren't harmful, and reject other things like the ones mentioned that don't cause any direct physical harm, but are still immoral. Why would they be immoral? In such a system they would probably be more "pragmatic" than immoral.
Well, how do you define morality?
Personally, I don't see how an edict from some deity could possibly define right and wrong, so we still need to find some sort of rational basis for
any moral system.