Can objective morality exist in Atheism?

[tavarish]

Then how do you (Atheism) rationally justify making a moral claim?

I'll go out on a limb and say you don't believe in the fairies in my underpants drawer. How does a non-believer of fairies justify making a moral claim?

All of us are subject to the morality of our respective societies coupled with our own personal experiences. We build up tolerances and preferences as to what we'd like to do and what we'd like done to us.

Ok, buy why is that "principle" valued as opposed to one that says, "do unto others before they do unto you?" (the selfish rule)

The reason it's valued is because it actively promotes the proliferation of the species. It is a mechanism that has developed through evolution. It is very possible some did not have this instinct, and thus did not procreate as abundantly as those who did.

We have people like that today. They actively want to inflict harm on others. This is masochism and sadomasochism.

The process of natural selection has all but taken care of those who live life by the selfish rule, and the fact that we exist and continue to procreate in large numbers shows that it is a favorable trait to possess.

This is an equivocation making "survival" and "golden rule" the same thing, and serves only to muddy the issue you are trying to explain. If 'survival' is the goal, again I ask why? Why not adopt a value that says kill them and take their food? Why is the 'golden rule' chosen as opposed to the selfish rule?

Not ONLY survival. Survival and procreation - I'm pretty sure I wrote that. If you killed everyone the species would go nowhere and there would be no one with which to mate. Indeed we do still see people who react selfishly, which means that those individuals most likely lack proper psychological development or suffer from a chemical imbalance.

The golden rule is absolutely paramount to the continued survival of the species, not just to certain individuals.