Where does the Bible say the earth is flat? (It's not been part of the Church of England teachings that I've been exposed to.)
If you read it literally, the bible says all kinds of silly things that modern churches conveniently overlook. Not only is the Earth flat, but it doesn't move (hence the problems with Copernicus) and was created in three days (before the stars in the sky).
While factually incorrect, this is one of the least objectionable passages in the bible IMO. At least it doesn't advocate forced marriage for rape victims, or slavery, or murdering your enemy's children. But some churches are quite adept at explaining away these little problems and trying to find the "underlying truth" in scripture. You know, like how abortion is an unforgivable sin and god hates fags. The point of which is just to say that it's an old text, written in a different time, by people with their own cultural biases just like we all have our own cultural biases. I don't think you can take it very literally, and I certainly don't look to it for moral guidance, but it's still an important part of our cultural history and collective mythology. I think people should read the bible (warts and all) just like they should read Shakespeare, because of the huge influence these works have had on every facet of American life.
But if you believe that the Earth is flat, in my mind it's only a tiny step from there to believing in Macbeth's witches or Jesus's miracles. The supernatural elements are there for dramatic impact, and aren't to be taken literally. The danger of the flat-earthers is that they don't recognize the magic required in their beliefs, and so can go about their daily lives laughing at people who believe in ghosts and telling themselves that they are the rational ones because of the evidence of their own eyes.