1) Objective moral values
There needs to be a way to distinguish what is good from what is bad. For example, the moral standard might specify that being kind to children is good, but torturing them for fun is bad. If the standard is purely subjective, then people could believe anything and each person would be justified in doing right in their own eyes. Even a “social contract” is just based on people’s opinions. So we need a standard that applies regardless of what people’s individual and collective opinions are.
They may be justified in their own eyes, true enough. But why should, for example, the opinion of a violent thug's justification of his own actions matter to those of us who desire the keeping of a peaceful and compassionate society? They would find no justification among us. There is practical no need for objective moral dictates to uphold such a society if our preferences and values naturally align; our subjective values are toward its (our) preservation.
2) Objective moral duties
Moral duties (moral obligations) refer to the actions that are obligatory based on the moral values defined in 1). Suppose we spot you 1) as an atheist. Why are you obligated to do the good thing, rather than the bad thing? To whom is this obligation owed? Why is rational for you to limit your actions based upon this obligation when it is against your self-interest? Why let other people’s expectations decide what is good for you, especially if you can avoid the consequences of their disapproval?
From a pragmatic standpoint, there would be the law, but supposing I could get away with doing something I feel is wrong, I wouldn't do it because to abstain aligns with my preference to do what I think is right. My preference to do something for the good of others and not merely for myself would outweigh a selfish "wrong from their (our) point of view". This is altriusm shaped by who I am and how I was conditioned. If that is my preference, then I am rational in behaving in accordance with it, and I would be irrational to behave against that preference if it is truly my preference.
3) Moral accountability
Suppose we spot you 1) and 2) as an atheist. What difference does it make to you if you just go ahead and disregard your moral obligations to whomever? Is there any reward or punishment for your choice to do right or do wrong? What’s in it for you?
Pride. I can succeed and find happiness without the need to tread on other people. I prefer that knowledge to potential success with respect to my other preferences through the alternative.
Moreover, if my values lean toward creating prosperity for myself and others, these will be my reward.
4) Free will
In order for agents to make free moral choices, they must be able to act or abstain from acting by exercising their free will. If there is no free will, then moral choices are impossible. If there are no moral choices, then no one can be held responsible for anything they do. If there is no moral responsibility, then there can be no praise and blame. But then it becomes impossible to praise any action as good or evil. Many atheists hold to determinism and there is no free will.
I do not know whether there is free will or not, but even if there were not, it would still mean that those who are insufficiently aligned with doing "good" by the rest of us would still be rationally detained since they are working against our preferences. Of course, the trick is to do so in a way that wouldn't violate our own values.
5) Ultimate significance
Finally, beyond the concept of reward and punishment in 3), we can also ask the question “what does it matter?”. Suppose you do live a good life and you get a reward: 1000 chocolate sundaes. And when you’ve finished eating them, you die for real and that’s the end. In other words, the reward is satisfying, but not really meaningful, ultimately. It’s hard to see how moral actions can be meaningful, ultimately, unless their consequences last on into the future.
What does ultimate meaning matter, if something definitely matters today? You may die tomorrow, but that doesn't mean that the enjoyment and value of what you are doing today doesn't and shouldn't exist.
Theism rationally grounds all 5 of these. Atheism cannot ground any of them.
Explain how theism rationally grounds any of these.