I don't know that I would agree that they "hate" it. Their job is to make sure that you learn the basic skills needed to get through life. That's difficult with 100 percent of your attention. It would be impossible standing in front of a classroom of people on Facebook.
Your teachers simply realize that in your future you will have to support yourself and they're trying get you ready for that. Their concern isn't about Facebook, it's about you.
If you doubt what I'm saying, look at the jobs listings and see if you can find one employer that's looking for people who know how to use Facebook.