Addendum:

About atheists vs theists and undergrads vs philosophers, I think two-boxing is a position that preys on your self-image as a rationalist. It feels like you are getting punished for being rational, like you are losing not because of your choice, but because of who you are (I would say your choice is embedded in who you are, so there is no difference). One-boxing feels like magical thinking. Atheists and philosophers have stronger self-images as rationalists. Most haven't grokked this:

How can you improve your conception of rationality? Not by saying to yourself, “It is my duty to be rational.” By this you only enshrine your mistaken conception. Perhaps your conception of rationality is that it is rational to believe the words of the Great Teacher, and the Great Teacher says, “The sky is green,” and you look up at the sky and see blue. If you think: “It may look like the sky is blue, but rationality is to believe the words of the Great Teacher,” you lose a chance to discover your mistake.