There is probably no god, and even if there is, we live on an utterly insignificant speck upon an utterly insignificant dot in a universe in which the part we can observe is incomprehensibly massive and the part we can't was recently hypothesized to be 1-followed-by-a-hundred-zeros times larger than even that, so you'll forgive me for thinking it's unlikely that any god that does exist cares about our insignificant speck any more than any other. Even if you don't buy this, you must agree that we can't prove it either way, and that any "evidence" in this argument is more accurately characterized as conjecture.
So we live in an uncaring universe where we are utterly insignificant and there is nothing to care whether we live or die or how we carry out our lives. There is no meaning to any of it. We are here as the result of a cosmic accident. Our brains are wired to think that we're important as a part of our self-preservation instinct, but that's simply untrue.
As a result of this, I think it follows that we're all pretty much the same, and that we should all be equal. Furthermore, in a universe that doesn't care about us and all that we're absolutely guaranteed is that we have a limited time here, we should do whatever we can to maximize our happiness and prosperity for the brief time we do have. Since we're all created equal, and since socialization is an important part of being human, this means doing well unto others.
