Quitters of just about _any_ harmful habit will report all that. This doesn't mean that FB is harmful to everyone or even to a substantial fraction of its users. It's just that people who feel it is harmful for them are much more likely to "quit" it, and report improvement when they do. I bet people who just started to use FB also report more life satisfaction and less depression and anxiety. They made a change they felt they needed to make, in both cases.