In either case subtext is clear: "I have no respect for you, and I wish you would go away." You can say that as calmly and dispassionately as you like, but it's not really very sporting.

That's the issue under discussion, isn't it? The assumption of the adversarial mode is that if the other person loses their temper, it's because their position is weak. When presented with "Jesus is an invisible, magical, wish-granting friend," if the Christian doesn't have either a serious response or a clever quip, then they lose. It doesn't seem so much "I don't respect you" as "I disagree" and not so much "I wish you would go away" as "put up or shut up."