People thought the same about YouTube, but that turned out to be a brilliant (and very profitable) move.
Then again, they also thought the same about AOL/TimeWarner, and they were absolutely right then.
It's usually pretty futile to try to predict the future. I can see Zuck's reasoning with the Whatsapp purchase, though, and I don't think he's insane. He and Larry probably understand the structure of the tech industry a lot better than most people.
The way I see it: Facebook's edge is its social graph. WhataApp had independently built a massive social graph, just like Instagram did. Facebook simply cannot afford to not acquire these companies.
Google already had a solid youtube competitor. The primary reason for the acquisition was not for the userbase, but rather because youtube was being sued by the entertainment industry, and by google stepping in to take over and fight the legal battle, they managed to preserve the future of online video.
It was definitely the right move, but this situation can't be compared to the WhatsApp acquisition.
Then again, they also thought the same about AOL/TimeWarner, and they were absolutely right then.
It's usually pretty futile to try to predict the future. I can see Zuck's reasoning with the Whatsapp purchase, though, and I don't think he's insane. He and Larry probably understand the structure of the tech industry a lot better than most people.