I still dont think you can justify any of those as monopolies yet.

Snapchat, twitter, pinterest, reddit, youtube, hangouts/gmessenger, linkedin, skype/groupme, imessage, discord, kik, line, telegram, signal. Especially justifying Instagram, because facebook really made it what it is. WhatsApp MAYBE, but in reality what facebook is doing is owning both the US and INTL messengers, I dont think they overlap in a way that justifies splitting it up, because FB's US marketshare doesnt drastically increase from WA. Is it the justice departments job from to allow the most popular domestic product from merging with the most popular international product? Uber being able to swallow up or own shares in all these regional services should be questioned then. FB/WA still have viable competition from imessage, snapchat, and skype.