User wiploc at talkrational tells the Parable of the Pawnbroker:

I was a pawnbroker… This guy came into my store, drew a chain out of his right-side pocket, and said, “How much will you give me for this fine gold necklace?”

…I politely looked at his necklace. It was fake. I pointed out to him the chintzy clasp, totally unlike what would be on a necklace of value. But he still insisted that it was real; so I cut the chain with a file, ready to test it with acid. But I didn’t need the acid: the inside was brown, not even gold in color.

The guy dropped the chain in his left pocket. He drew another chain out of his right pocket, and said, “This one’s the real thing.” This one’s the real thing? That was like admitting he’d known all along that the first one was fake.

I showed him that this one didn’t say, “14K,” like real gold would. It said, “14KEP,” meaning it was electroplate. It wasn’t even pretending to be real. But the guy still insisted it was real. So I cut it with my file, and showed him it was another fake.

Can you guess what he did then? He dropped it into his left pocket, pulled a third chain from his right, and told me that this one was real. I was happy to file this one too, ruin it, so he couldn’t try to fool anyone else.

He pulled out a fourth chain. He said it was real. I showed him that it wasn’t.

…First pattern: When this guy said a chain was real, that didn’t carry any weight. His apparent sincerity was an act or a pathology, not an indication of actual truthfulness. His saying something was legitimate didn’t make it legitimate, didn’t even increase the likelihood that it was legitimate.

Second pattern: This guy’s chains were fake. I had yet to examine his [next] chain, but I already believed it was fake.

I was willing to be surprised; if the chain turned out to be real, I would have accepted that. But I believed it was fake. And that was a justified belief, reasonable in the circumstances.

This story is analogous with my experience with Christianity. Somebody will tell me that the ontological argument is solid gold proof of the existence of Jehovah. I point out that it is patently absurd, and he pulls out another argument.

He doesn’t blush or backpedal. He makes no apology for having indiscriminately swallowed a lie and repeated it as a truth. He doesn’t tell his friends, “Hey, don’t be using thiss argument anymore.” No, he just tells me that the modal argument for necessary greatness is absolute proof of god’s existence. When I point out that this argument is no stronger than its opposite, the modal argument for the nonexistence of necessary greatness, what does he do? Is he taken aback? Does he say he’d better rethink whether his god really exists? Of course not. He pulls out another argument, and says, with all the sincerity of a seller of fake chains, “This one’s the real thing.”