Facebook for Kiddies?

My preteen asked me the other day why she couldn't have a Facebook account like many of her friends do.  I explained to her that Facebook has rules in place in regards to children.  The single most prominent rule is that a user must be at least 13 years old.  I also explained that I am uncomfortable with the kiddos having profiles on a social network that anyone can have access to.  Lastly, I have seen several of their schoolmates behave in less than exemplary ways on Facebook and I am not thrilled with my children being subject to that behavior.  Needless to say, she was unconvinced as to why this should stop her when it doesn't stop her friends.  As I listened to her tearful pleas to reconsider my decision, I felt as if I was a horrible parent for depriving my child of something that it seems many of her friends have.  It should be noted that I do not feel bad enough to change my decision though.  My question is this:  What would your decision be if your child wanted to create a profile on Facebook?  Why would you make that decision?