All Have Sinned
As a religious school they have a right to set standards. Standards expected of Christians. They do not have to tolerate thieves, liars, rebels or sodomites.
It is odd to be in a Christian school and be an open active sinner without repentance. I am not a Catholic, but the dirty secret is that we are all sinners and and need to believe in Christ to be saved. Then we are expected to live a holy life.