Why be good?

[Jenny A]

I'm not asking whether atheists can be good people or whether they are good people. Despite much of the rudeness and foul language directed at me (and others) in this forum, it should be obvious that atheists may strive to be kind, tolerant, generous and respectful toward others. And they do this because they recognize that "right" and "wrong" behavior is real and not theoretical.

What I am asking is: what is the BASIS for objective moral behavior? Where does it come from?

If some feel that they have already answered, my apologies; however, I re-phrased my OP based on a quick scan of a few responses.

I will try to get through all of the posts as quickly as time permits. Sorry for the delay.

Sorry but that is not even remotely what you asked in the OP:

If there is no God, then there is no hell; and if there is no hell, then there are no ultimate, eternal repercussions, good or bad, for how we live out our mortal lives. Of course, atheists insist that people should be "good without God."

But why? If God does not exist, why be good?

You originally asked why be good if there are no god made consequences?  To which many of us replied, there certainly are consequences for bad behavior right here and now, both for society as whole, the victim, and the person behaving badly.  And that further, evolution has given us empathy among other useful things which makes us generally want to be good.

Now you want to know how we decide what good is. That is a very different question.  Esquilax has already explained why it is that to answer god determines what good is, is not really an objective standard.  I would add that determining what god wants is a pretty subjective exercise in itself.  Christians all profess that this is the standard, but they don't all reach the same conclusions.  On the finer points the Bible can be clear as mud.  And there are various things in Bible (such as slave holding and stoning rape victims) that polite Christians simply ignore.  The reasons they ignore them are subjective.

We could invent objective standards like utility (the best outcome for the most people), selflessness (the best system for societal death under the weight of freeloaders I can imagine), might makes right (the ultimate authoritarian view), and so on. 
Such standards can provide a framework for talking about what we should consider right and wrong, but they don't entirely explain what it is we actually do think is right and wrong.

For example consider incest.  Most people have very strong anti-incest reactions.  Visceral reactions.  If pressed most people will tell you that incest is wrong because of possible birth defects.  But in point of fact, unless there are recessive genes likely to produce birth defects shared between the couple, there aren't any real objective reasons why we shouldn't commit incest. And if one member of the couple in infertile, there is no reason why they shouldn't have sex.  Nor are most people mollified if the couple agrees to have one of them rendered infertile.  So at least some of what we consider right and wrong has to do with visceral reaction, not reasons and standards.

I think that evolution has endowed humans, like all social species, with some basic morals, mostly based upon empathy and survival of the species as a whole.   Beyond that it's all societal evolution.   Which is to say, it's not the least bit objective, except that moral systems that survive, survive.  A moral system that produces a working society that can defend itself lasts, one that doesn't doesn't. There is a reason we should not return to the morals of ancient Judea.  That is being tried in the Middle East with rather catastrophic results.  Religious states fair worse than secular ones.  It's less clear whether secular states where most people are religious fair worse than secular states where most people are atheist.