Christian colleges are private entities - since they aren't part of the state, they can kick you out any time for any reason. Students who decide to go there (presumably because their religion is very important to them, or because it's cheaper or more prestigious than an alternative school) are choosing to follow the school's rules.

Don't get me wrong, we can certainly argue that a school's policies are draconian, or out of line with what most modern religions allow or expect of their adult members. But that doesn't mean we can stop a school from setting its own rules (within the bounds of the law), and they'll likely keep doing it as long as people are still signing up to go.