It's no good to say of Christians that they are "not rational." Any belief system is rational if one accepts the underlying presuppostions. There are numerous works of Christian apologetics that lay out the case for the faith in a rational manner. Nevertheless, one cannot be persuaded by argument that Christianity is true, because Christianity involves a personal relationship with God based on faith and repentence. It's a personal experience that the individual knows to be true without being able to prove scientifically. Arguments made to a Christian against the Christian faith, however rational and well-laid out and scientifically verifiable, must always fail, because of this personal experience of having a direct relationship with God; the truth of the relationship overrides even the most brilliant arguments against God.
It's also why the "argument from outrage" isn't persuasive. The Christian knows from personal experience that God is good. Therefore, He must have good reasons for allowing/commanding/committing acts that seem atrocious. Scott Adams, in his book Seven Years of Highly Defective People (which is a series of Dilbert comics with Scott's commentary in the margins) talks about the character of Dilbert's Garbage man being the smartest man in the world. He writes, "The unanswered question about this character is why he would choose to be a garbageman if he was the smartest man in the world. But if you think about it, we wouldn't be in a position to judge anything done by the world's smartest person. Obviously, his decisions would be different from our own--he's smarter! So if we don't understand why he does what he does, the problem is probably on our end."
In the same way, when we who are mortal and fallen don't understand the actions of a good and omniscient God, then the problem is probably on our end. Perhaps God was preventing a major eruption of trans-national genocide? How would anyone who is not omniscient know?