Maybe he simply isn't that confident in that opinion to state it so bluntly. I agree with the "reading between the lines" interpretation that this guy probably thinks facebook is a bad thing. But, thinking that, and coming out strongly with that position while holding such an influential position are two very different things.

If I had such influence I'd certainly be hesitant to just go all guns blazing, and I'm someone that strongly believes social media (primarily facebook) is a serious threat to civilized society.