All opinion, no sources: I've always considered it as a defensive play rather than a positive one - Facebook have this beautifully well-entrenched network effe

All opinion, no sources: I've always considered it as a defensive play rather than a positive one - Facebook have this beautifully well-entrenched network effect that defends their position - their unique selling point is that they know the world's social graph, and it's terribly difficult for anybody else to try to build that data as long as Facebook provides an acceptable alternative to any new communication medium, because it's always going to be easier to engage with your friends on a platform they already use. In WhatsApp's case, though, Facebook screwed up - they didn't offer a mobile messaging service that was convincing enough to take the easy victory that their position should have given them in that market, and that chink in their armour let WhatsApp build a social graph and a toehold in the space that could have made them a true competitor, so Facebook paid to make the mistake go away.