Be it messengers, social networking apps, eCommerce stores, ERP software, anything - If we choose one organization to rule them all, it won't be very long before they start showing the traits of that one Saruman's ring that rules them all.
Facebook, by doing things like this, will only hurt themselves. We've been down this road before with Microsoft. It is anti-trust, and will get them in a lot of trouble.
We the people have invented these authorities a long time ago precisely because we the people suck at making individual decisions to improve global outcomes, and we need to organize ourselves in institutions such as these to fix things.
http://www.eater.com/2015/11/25/9800584/google-burying-yelp-...
http://au.idigitaltimes.com/google-pushes-yelp-and-amazon-do...
http://www.fairsearch.org/yelp-ceo-stoppelman-criticizes-goo...
Of course that's just the obvious consequences, ignoring the larger implications of allowing companies to place arbitrary restrictions on their services - when at the same time those services become more and more critical infrastructure.
This is fine.
However online communication is different. Imagine if the telephone company would bleep out any time your friend mentions a competitor's company. You'd never know a competitor exists. Especially if that competitor is up-and-coming and doesn't have the pockets to send flyers to every damn house in the state.
I think it's slowly high time the anti-monopolistic regulation looks into their business practices and starts considering cutting them up into discrete companies per market.