Unfortunately that isn't going to work, in my experience. If someone is that convinced by what their faith tells them, you're almost never going to get through to them. On another forum I'm on, there is one particular poster who has come out with some (to him) perfectly reasonable and rational ideas that sound insane to me.
For example, his God is good, therefore anything he does must be good, since God is good and by definition cannot be bad. So, all the smiting, blowing up of cities, attempting to kill every living creature on the Earth .. all good.
I blow up a city, I'm a mass murdering sociopathic maniac. His God does it, it's good.
How exactly do you argue with someone like that?