Mobsters will fight over existential threats too, and it doesn't make what they're doing appropriate or worth defending. I'm not sure I'd go so far as defending to the death Facebook's right to be a giant conglomerate eating up other companies. Isn't that exactly the point?

I don't see an argument saying 'companies must be ever bigger, infinitely, as a moral right'. The companies might think so, very passionately even, but I would suggest they're wrong and it's a bad thing to indulge.