While I do understand that principals are under enormous pressures from many different angles it seems to me that your frustrations about Facebook are from primarily negative experiences.
Students who use Facebook to bully and harass others should be dealt with strongly and that is covered in your discipline policy somewhere at the school or district level. Or even the police if needed.
No doubt students and parents misuse Facebook in ways to slam teachers and schools on a regular basis. Is this any different than the coffee crowd getting together to complain? The coffee crowd is now on Facebook. Let’s meet them online instead of hearing the gossip at PTA meetings and in the stands at basketball games.
If you were my principal I’d want you to embrace Facebook as means of positively promoting the school with our own school page, and working with teachers to reach students with their own class pages.
Fscebook is where students and parents are. If you model appropriate use of it from the school it sends a message to all in your community. Get parents to post comments on the wall about he awesome things they think about your school.