Topic: All Is Permitted
I've found discussions of morality to be in fact the most frustrating of any conversations one can have with a believer. You'd think after all those years of going to church and reading the scriptures, they could enlighten us poor, lost wretches with some solid insight on at least the one thing that God supposedly can do better than anything else: tell us about right and wrong. For the record, I don't think all theists hold entirely absurd views on morality. But I do think it's uncommon to run across a believer who has put any effort at all into understanding the meaning and consistency of their moral positions. And that not only reflects poorly on themselves, but the institutions educating them. I don't think solving the problems within ethics is trivially easy for the atheist at all and I can't say that I have any final answers. What I do think is easy, is responding to most Christians. A couple of these deal with meaning and purpose since those things often get tied up in moral conversations.
Confusing incentives with imperatives
Believer: Without God, you can do anything you want!
Atheist: But can't we do anything we want though, with God?
Believer: Yes but, the wrongdoers without God will ultimately go unpunished.
Atheist: So if they don't get caught, that makes it ok?
Circular
Believer: If there is no God, who is going to give us rules to live by?
Atheist: I, Gadianton will give you rules to live by.
Believer: But you're not God!
Atheist: True, but God isn't Gadianton.
Incentive cuts both ways
Believer: Without God, there is no eternal incentive, people will not as readily feed the poor and help the needy.
Atheist: Without God, there is no eternal incentive. Without a harem of horny virgins awaiting, young males will not as readily crash planes into buildings.
Criteria confused
Believer: Historically, the good done in the name of God outweighs the bad!
Atheist: Great! When did you become a utilitarian?
All or nothing
Believer: If I can't live forever with God, what's the point of living at all?
Atheist: If I can't make a million dollars a week, what's the point in having a job?
Objective meaning is absurd
Believer: My life has meaning because God put me here for a purpose.
Atheist: Do the lives of pigs have meaning because farmers raise them for beacon?
or
Atheist: Do the damned find meaning because God predestined them to hell?
or
Atheist: Does your life have more meaning when your parents tell you what you have to do?
Ignorance
Believer: God can look beyond the limits of man's reason and tell us what we should do.
Atheist: Case in point: The Lafferty brothers.
Believer: No! What they did is sick and makes absolutely no sense!
Atheist: God works in mysterious ways, I didn't expect you to understand.