Separation of Church and State exists to protect the state from the church as much as it does to protect the church from the state. The founding fathers wanted two things: no king, no pope. The force of religious instutitions is much more right-wing than the force of religious individuals. Listening to Pat Robertson talk is very different than listening to, say, my church-going neighbor.

So, people aren't expected to drop their morality (if indeed that's even possible) but they are expected to serve in favor of _all_ people and not just of their own church leaders. The church was the original lobbyist.