Is it really a surprise that this what she grew up to be? She was a child star. She was pretty much owned and marketed by a major corporation. She never had an actual childhood; She was always working. The media/public has been picking her apart since she was 13. She made an obscene amount of money. Her parents see her as their "cash cow". She had "handlers" instead. Most of the friends she had were people that worked for her. It would be a miracle if she ended up well-adjusted.
I watched this video of her once, when she was a teenager...She was sitting at the computer, answering questions from fans. And everything that came out of her mouth was met with hysterical laughter from her handlers. Just like the simple little thing...*laughter*. Just imagine always being surrounded by people who laugh at everything you say. You are the funniest person in the world to them. You are always right. That's what happens with these child stars. They are always being praised. No one tells them "No".
The public is desperate for this girl to fail. People have been talking about her apparently inevitable sex tape, rehab trip, arrests, etc since was 15. With this performance, people feel they are closer to all of those things, so they salivating.