A Naturalistic World

[Alan V]

I'm more interested in arguing your theist friend. Here's a guy who seems to be saying that if God changed his mind about something, that would change the absolute rightness or wrongness of it. But how could that be? Would (or could) murder become acceptable moral behavior based solely on God's say so?

Actually, he is an atheist friend who was echoing a theistic-style argument.  I assume he hasn't been involved in many atheistic arguments about morality, or he wouldn't have made such an over-simplified argument.

And yes, many theists do believe that if God ordered them to murder, that would make murder right.  You only have to read their holy books to find that out, although many modern believers are probably quite thankful they hear no direct commands from God these days.  

Even then, we more secular types typically have our own justifications for killing other people (in wars, by the police, to save other lives, or whatever).