One of the problems with this 'anything christian is good and anything athiest is evil' idea is not so much in how people expect their peers to behave, but how they expect people of authority to behave. People expect politicians, teachers and popular leaders to be 'good people', and thus they are expected to hold strict Christian beliefs.
Thus a politician who declares herself to be an atheist is unlikely to become popular, because they will be seen as being slightly evil, or at least amoral. Even a politician who declares themselves Christian can be suspected of being slightly 'unchristian'.
This in turn hurts liberal and other non-christian beliefs such as the pro-choice stance and homosexual rights. This also suggests why creationism is more popular than one would expect; anyone speaking out against it is declaring their own beliefs in the falsity of the bible.