Obviously, I don't have a problem with being on FB. My church has a FB page. What you have is not a problem with FB. Its controlling the effects it has a the venue of a Christian school. Its not the position but the direction that is a concern of the church. Let me explain.
You know, we adopted kids out of foster care. Often I would correct one of them for actions that seemed harmless enough to the passive observer. But I knew my kids. People would say, "Why are you so hard on them?" My response was, "Because I know where this is going."
We never let our kids on social network sites. My kids didn't have cell phones until they graduated high school. Actually, there are a lot of private non Christians schools who have the same ban.
If I'm famous for one saying, it would be, "Everybody likes my pie but nobody wants my recipe." The school is a school, not a home. It has to operate in a different perameter with different objectives. My advice to you is, trust the recipe; it works.
For those angry detractors, I would simply say, its a private school. If you don't like the rules, don't send your kid there. I hope you know we love you and your family. I hope you don't take too much flack from either side. Whatever happens, walk with God. Take care."
If thou hast run with the footmen, and they have wearied thee, then how canst thou contend with horses? and if in the land of peace, wherein thou trustedst, they wearied thee, then how wilt thou do in the swelling of Jordan?