I'd work on nukes before I'd work at Facebook. Nuclear weapons have arguably prevented WWIII, at least so far. Conversely, if WWIII ever does come, I wouldn't be surprised if Facebook has something to do with causing it.
Facebook is driven internally, from the top down, to accomplish murky, exploitative goals that are in the interests of nobody except the company and its shareholders.
That's why Facebook is worth hundreds of billions of dollars while Reddit can barely pay for their own bandwidth and Tumblr gets passed around between acquirers like it was a radioactive waste dump that runs a porn business on the side.
I don't know WTF Twitter is worth, if anything, but some people seem to think it's got a viable business model, so meh, whatever. They aren't Facebook.