It's entirely appropriate and reasonable to say "I don't understand why Facebook would do this; please explain it to me." But it reflects a supreme lack of humility to say "I don't understand why Facebook would do this; they must be idiots, and when they, armed with inside information I don't even know I don't have, come to defend themselves, I will angrily try to convince them of the error of their ways."
If you think what Facebook has done here is stupid, why is that something to get upset over? In fact, why is it even something worth arguing about? You're not going to convince anyone who matters, and anyway you have nothing to gain by doing so: Instead, just short Facebook stock and be smug in the knowledge that, when Facebook announces next year that they're abandoning PHP in favor of a ménage à trois of OCaml, F#, and Clojure, you'll be able to say "I told you so".