A Christian left a fabulous comment on one of Sisyphus Fragment's blogs, with this irrefutable logic:
Actually, you interpreted Romans 2:15 incorrectly. (I find it amusing when atheists try to interpret the Bible, because the Bible itself says that you cannot know the mind of God if you do not have his Spirit, 1 Cor. 2:14-16.)This is absolutely marvelous – if we disagree with a Christian about his/her religion, we're inherently wrong, because only Christains can interpret the Bible correctly!
It's amazing to me how pervasive circularity is in the Christian religion (and others – I just happen to be picking on this one guy today). We see it everywhere, it pervades all aspects of the religion. Any time you try to have a serious discussion with a Christian, you quickly get dizzy trying to follow the logic.
Circular hermeneutics. I love it. To understand, you have to believe. Once you believe, you can understand.