If Facebook broke the law, great. If they didn't, the prosecutors need to convince the American people & judges that a law was broken or should be written to fight against whatever Facebook is doing wrong.
Stratechery's writing on 'aggregation theory' is relevant here. How can you have a monopoly when the web is open? I'm merely playing devil's advocate here but I deleted my Facebook account in 2012 (after joining in 2007). I could still call my parents, email my friends and send text messages. Facebook didn't have a monopoly on communication. I was an instagram user as well but stopped at the same time and I stopped using Twitter but the point is, just because Facebook buys every competitor doesn't make them a monopoly. the web is open and free, can't another company just come up and take over?