what are we supposed to say again when christians ask us where we get our morality?

[max-greece]

It may be incomplete but it isn't arbitrary.

No, it totally is arbitrary. I could just as easily stipulate that morality is defined as whatever is most painful to other sentient beings, whatever is best for non-sentient beings, whatever is best for myself over all others, whatever is best for my children over all others’ children and so on and so forth.

Still not arbitrary. If you could show there was benefit for the species from any of the alternative moralities you suggest then you might have had a point in suggesting they were valid. Evolution through natural selection gave us the basic properties from which we formed out moralities. It can't be any other way.

Our evolved senses, as I stated in a previous reply in this thread, of empathy, reciprocation and a basic sense of fairness determine what is good and bad, in the main.

This is an example of the “is/ought” fallacy, you cannot reason from the way things are to the way things ought to be.

You will have to explain how empathy, reciprocation and a basic sense of fairness fail to provide your "ought." As I see it, unless I am misunderstanding you, that is exactly what they give us.

Secondly, apparently we’ve also evolved the ability and desire to mass murder one another, rape one another, lie to one another, and torture one another. Are all of those things therefore morally good actions?

We have evolved the ability to overcome our instinctive morality along with other instincts too. This should not come as a surprise, and it isn't all bad news. Heroism, for example, is the over-riding of our strongest driving force - self preservation. Things cannot be morally good if they are not in the interests of the species and there would have to be exceptional circumstances for them not to be in the interests of individuals or groups.

At the same time we have to recognise that one of the best ways to get people to behave immorally is religion. Difficult to get people to fly planes into buildings without it.

If morality is a particular system of values and principles of conduct then one can say that such systems are universal (amongst human populations). One cannot say, however, that the actual values and principles are universal.

I guess we have a different definition of Universal. Who gets to stipulate their morality? The individual? Family? Society? Species?

I am not sure we do define universal differently - I just don't accept it as a concept. What I provided was as close as I can get - although a case could be made for including other species.

Societies get to dictate their moralities. Families and individuals get to define their's within the parameters of those of the society.

History judges how well or badly they did.