One of my readers is an expert at the moral argument, and wrote a number of articles about his experiences talking to non-Christians about it. He comes from a liberal Christian background, so his views and experiences are not the result of growing up in a conservative Christian environment.
In the first article, he talks about what theists mean when we say that atheists can’t rationally ground objective morality:
They misunderstand us to be implying that they are immoral people. But this is not at all what we are saying. Since we believe that the moral law is incumbent upon every human, and is woven into the very fabric of our souls, we are not at all surprised to find even atheists dancing to its tune (to mix my metaphors). The fact that atheists very much want to be thought of as good people is only a tacit admission that they understand that there is such a thing as “good” and that it is good to be good. But if morality is merely a human convention, then the most that an atheist can be claiming is that they are morally fashionable.
There’s no moral credit for doing that.
In the second article, he talks about whether atheists can “reason” their way to correct moral views, if their conception of reality says that the universe and humans are accidents:
A chance ethical system cannot do the trick if it is true that there are right and wrong answers. If there are indeed objectively right answers to moral questions, then reason is certainly an ally, since it can help us to assess the conditions and marshal our intuitions, but it does not in itself make the answer right. Neither does an ethical system make right answers; it can only (if legitimate) help us to navigate through real passes with real reefs and currents. But you could never say that any ship of history had hit a reef unless you were first willing to admit that things such as ships and reefs actually existed. That’s a very big pill to swallow for anyone committed to a purely material world, where truth and ethics extend no farther than the will and imagination of the biochemical flukes we call “humans.”
In the third article, he takes on the argument by atheists that much of the moral evil in the world is due to theists:
When asking whether a behavior is caused by a belief system it must first be determined if that behavior is consistent with the beliefs in question. For a religion like Christianity there is some hope of doing so, since it is founded upon certain doctrines and is in possession of a guidebook — the Bible — to which one might appeal in making a ruling. For this reason a strong case can be made that most of what is commonly credited to Christianity is actually a violation of its fundamental principles. It is not consistent with Christianity; it is antithetical to it. And if something is inconsistent with a thing it is hard to make a case that it is caused by that thing.
In the fourth article, he talks about how atheists misunderstand the purpose of acting morally in Christianity:
The irony is that Christianity does not even teach that we win heaven by virtue of our good works. In fact, it may be the only religion that explicitly rejects such an idea. For example, Islam actually teaches that our good deeds must outweigh our bad, and Eastern religions teach that we must work our way to enlightenment through various moral and spiritual practices. By contrast, Christianity teaches that we must put aside our futile thoughts of measuring up to God’s perfect standard and throw ourselves upon the mercy of His court. We have but to accept, as spiritual beggars, the provision He has made to cover our sin and win our righteousness in Christ.
Good works come as a result of our love and gratitude toward our creator and redeemer; they are not the cause of our redemption. The Christian ideal is to be good for God’s sake, not for the sake of what He can do for us. God is not to be confused with Santa Claus. To think otherwise is to make the mistake that Satan made regarding Job’s motivation for righteous living (Job 1:9-11).
In the fifth article, he talks about whether atheists can rationally ground the claim that they are “good” at morality:
As it turns out, most atheists who like to think of themselves as moral do so with a sense that they are saying something particularly meaningful. The implication is that they have access to moral knowledge that they are committed to put into practice. It is something like saying that you are a good baseball player, which refers to a particular game with known rules and objectives that you skillfully follow. If this is not true, then a moral atheist is just asserting that they follow their own desires; they are saying little more than, “I do what I feel like doing, and whatever I do I call ‘good.'”
It might be a fun activity to read these posts, then find an atheist and ask them whether they are a good person, and what do they mean by “good” and “evil”. Ask them whether they are making free decisions, and how can that be possible if they are just made out of matter. The moral argument is the most accessible argument to discuss with non-Christians.