Do atheists even need an objective moral system?

[genkaus]

The only important aspect, I should think. We have no moral obligation to rocks or other inanimate objects. We can use terms like "wasteful" or "foolish" but you can't be cruel to rocks or other things that don't think or feel.

We have a moral obligation to ourselves - the most important aspect that you completely ignore. Our obligations towards other would be derivative to this one.

Usually I invoke The Social Contract. I am honest with others because I wish them to be honest with me. I respect the rights of others because I wish them to respect my rights.

Now, we can have a debate as to what those "rights" are, who's "rights" trump who's, and whether or not lying might be justifiable in certain circumstances and this is where morality gets more "subjective".

This is where your self-contradictions become apparent. You continue to refer to morality as subjective and yet assume the principle of universal moral reciprocity. The obligations created by the social contract would be moral in nature and would require the parties to agree upon the same moral premises. You can't use it to then justify morality. That's using a circular argument.

What if the data wasn't so clear cut? What if the outcomes were mixed?

Oh, you mean like in science where we give the margin of error and our evaluations reflect both positive and negative outcomes, grade their relevance and then indicate whether the overall outcome is positive or not? Yup, still objective.

What if one thing was gained at the price of something else? Here is where it gets subjective, that we value certain things over others.

As long as our valuation is based on reality as well, the evaluation would remain objective.

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Well, in order for people to behave properly, they need some rules from the top brass.
Currently, these come mostly from a country's laws.
Most countries adhere more or less to the same laws so one could argue that this common group of laws could be an "objective moral code".
Objective because it is not the view of one single person or single group of persons, but what diverse and independent groups decided to be their guiding rules.
This "independency" may be challenged, given that, for example, the original US laws were adapted from European laws, which were adapted from roman + christian + jewish + (a bunch of others) laws .. but you get the picture... independent as non-communicating with each other.

That's my view on "objective morality".
Anything else is subjective.

That's not objective morality - that's objective legality. What about the rest of it?

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But if God can determine objectively what is moral, then these facts on which such objective determinations are based, are presumably out there to be discovered potentially by anyone else. God becomes unnecessary to the process and morality exists outside of God's will. Thus, the theist hold no stronger ground.

That has been my point all along. Whether or not god exists is irrelevant to the question of objective morality - no matter how loudly and forcefully a theist shouts otherwise.