Thats kind of a misconception. They often use source material that is vague and unclear so first they have to make up a "literal" interpretation before they can unyeildingly believe it. It's no more literal than anyone else who interprets vague religious texts; the interpretation is still heavily infected with their own personal slant.
I bet this guys wife cheated on him under the christmas tree. "But honey, the jizz you swallowed is still affecting your brain" must've been a fun conversation.