While friends and coworkers who work(ed) at facebook have had a much better time, with far more perks, interesting projects work not thrown away and a much better work life balance.
I think there are already more than two dozen smaller niche social networks.
Sources for McDonlads replacing all other restaurants. Maybe you haven't traveled as much but for me I always check out local McDonalds, hardly actually eating there. One of the reason they have been successful is adopting local tastes. Costa Rica has Gallo Pinto in addition to fries as options. Serbia has this crazy Crispy meat thing.
With McDonalds I know what the product is and I pay for it. With Facebook it's a little less clear what they are doing. One certainty with FB, we are the product.
With FB they are a little nefarious, especially the Free Basics thing. Google is doing similar things with Google Fiber and the defunct ballon idea.
If people cared about privacy that much, they should use some other network. People weigh the trade-offs of benefits vs costs and still choose to use FB and Google.
It's why we should criticize the actions of any power (whether the Us, China, the EU, Russia) to control citizens and eliminate smaller cultures. Maybe melodramatic but it's exciting. The growth of Chinese networks is interesting, wonder how they would develop under a democratic government? Further innovation or do they only exist because of that environment as you suggest?