It's also rather difficult to discipline a child that would turn around and threaten the parent with a social services report for abuse.
I'm the oldest of eight... my youngest brother tried that stunt when he was 14; I was visiting at the time of the incident, and the little punk was acting out, thinking he was a badass (all of us boys did that, and we all learned the hard way that the old man will call your bluff without hesitation). Anyrate, the cops did indeed show up, and my old man told him exactly what happened, and then said "...and if he wants to go into foster care so bad, I'd love to drop him off into it right about now." The cop laughed. One of my sisters immediately chimed in and asked if she could have his bedroom after he leaves, and another offered to help him pack. I just sat back laughing my ass off, as my little brother's face turned rather pale.
Needless to say, the officer politely declined, and after he left, *everyone* looked at the poor kid like he just screwed up big-time. I offered to take the little guy out back and have a chat with him, and my father agreed (I was 24 at the time); 15 minutes later he was apologizing from the bottom of his very soul (though he still wound up grounded for two months).
Mind you this was in Arkansas, where you were practically allowed to beat your kids to within an inch of their lives if needed, so YMMV.