Do I have to be called a Christian?

I stumbled upon an article today. It deals with a private Lutheran High School that expelled two girls for supposedly being lesbians.

The school had the legal right to do it since they're not a business and therefore don't have to abide by anti-discriminitory laws. The school expelled them because they concluded that the two girls were lesbians. They never engaged in any homosexual conduct while at school, but apparently their conduct outside of school is fair game for their expulsion.

I don't believe that homosexuality is right. I also don't believe that the actions the school took against these girls is right either.

If the school is going to expel these girls for engaging in homosexual behavior in their private lives, then why not expel those who engage in premarital sex as well? While they're at it they might as well expel students who have gotten drunk, lied, or coveted someone else's belongings, because we all know that real Christians never sin. (That was a sarcastic statement in case you
didn't catch it.)

I really don't think that expulsion was the answer. How are Christians supposed to influence others when they're constantly finding ways to push them away?