Bismark, I do believe that Christian Schools have the right to be Christian. I do not believe they should single out certain behaviors. Jesus said the greatest commandments were, "to love the Lord your God with all your heart, with all your soul and with all your mind"..."And to love thy neighbor as thyself". How many of the students or teachers are following those to a "T"?
I think if a student is openly doing something that is against the private school's code of conduct then the private school should be able to expel a student.
For example, if a private school has a policy against swearing then the private school has a right to expel a student. I would hope that if it was an accidental slip up, the school would give someone another chance. However, if it happens all the time then I think a private school should be able to expel for that reason.