When empires crumble they slide slowly at first, then the temple walls come crashing down. Facebook is not quite at the latter stage yet, but you can hear the creaking in the pillars and lintels. This week, the social media giant suffered two blows: an outage which took down its platform, along with Instagram and WhatsApp, and an expose by a disillusioned ex-employee who accuses the company of saying one thing about social responsibility in public – while behaving quite differently in private.