Why do so many Christians seem to think that..?

If you know that only a small minority of Christians believe that why would you say in your question "so many Christians"? You do not address your question to the small minority, but rather the general group. As such you are making the beliefs of a small group as representative of the body of Christians. There is a small group of atheists who have said at various times that while they do not believe in God, they believe in a spiritual afterlife and in miracles. Would it be correct of me to assume that these beliefs are representative of all atheists?