Facebook needs to avoid that at all costs, so is prepared to pay whatever it takes to acquire potential rivals, thus removing the threat.
Sadly, I remember the days of Microsoft's near-monopoly on desktop computing, and I'll be getting rid of whatsapp within the week. On to Telegram or whoever is willing to make an identical app that isn't owned by FB or Google or whoever. The question will be whether I can convince others to switch.
seems to me that whatsapp is more of an active "keeping in touch with friends" where facebook's forte is more of a passive "keeping in touch with friends". that would make them fairly harmonious in my book -- hence the autonomy.
But I guess Facebook acquiring them explains it: I don't use Facebook either, so now I'm even less inclined to use WhatsApp.