I think comparing bitcoin to facebook is kind of like comparing apples to oranges. Bitcoin is a P2P "currency" while Facebook is a social network. The uses of the two platforms are just too different
Apples oranges, sure. But it's also like comparing money to a website. Money just seems inherently better and far more potential to be bigger.
I think OP wasn't saying that they both are same, I think he meant in popularity Bitcoin will be bigger than what facebook ever was.