Only my opinion but, Facebook will find a way around this. An easy strategy will be to annoy the users enough that they opt-in. For example, want to post a pic? It's seamless if you are opted-in, but your not, so click through these 10 screens while we explain why you should opt-in. Every time you post a pic, you have to view 10 screens. Most people will just opt-in. They won't quit the service or deal with the annoyances, they'll just opt-in.