How?
It opens up the perfect opportunity for some competitor burning VC cash to swoop in and grab a ton of market share in a hurry, with a free iOS app.
FB knows this, so yeah, it's a completely hollow threat. But, just the idea that one of the tech giants has been backed into a corner by the risk of competition from paying-for-marketshare VCs or operating-in-the-red-on-purpose other tech giants, is really, really funny to me. No fun, eh Facebook? Hahahaha.