I don’t know if it’s an original idea, but I love the way Blonde Nonbeliever phrases this:
If you have a Bible on your bookshelf, you may be a Christian.
If you have a Koran on your bookshelf, you may be a Muslim.
If you have a Torah on your bookshelf, you may be Jewish.
If you have all three, you are probably an atheist.
Her message is spot-on: Only when you step outside your religion do you realize how alike all religions really are.