Anselm, who lived during the eleventh century, came up with one of the first Western arguments for the existence of god. Couched as a prayer he argued that nothing greater than god could exist and since a god that did not exist was not as great as a god that did exist, it stood to reason that god existed. Criticised at the outset it remains better as a prayer than as an argument. Because it only argues in a circle, how do we know that existence is a ‘great making’ property of anything, and just because we think it is doesn’t mean he exists at all etc.
But a lot of people love this argument, still use it and they made Anselm a saint to say thank you, and by all accounts is made him very joyful to have thought of it. That is because it fitted his world view and suited his logic. No amount of obvious flaws would ever have dislodged his belief anyway without the argument.
If you and I showed our birth certificates to anyone they would accept that we were born when and where we said we were. But apparently one third of Americans have a world view in which Obama being a Muslim and not being an American citizen (something journalists and his opponents would have known years ago and something the form filling to run for offices would have shown at his first attempts) fits and they will not drop the belief for any fact given to them.
This ability to run from facts because they do not accord with one’s belief has caused most of the bloodshed of the ages.