When I was interviewing at Google I decided to ask everyone I talked to what the point of Google's existence was, because it wasn't obvious to me, and I thought I'd get interesting answers. And it didn't work. All of them quoted from the mission statement: "to organize the world's information and make it universally accessible and useful".
So I should have read that before coming. The real issue, and I never really was able to ask the right questions to get at this, is that Google doesn't actually make money doing that. It spends money doing that, and makes money as an ad broker; thus the Wall Street Journal doesn't refer to "information organizing giant Google" or even "search giant Google" but rather "advertising giant Google". There's a trend that's been growing for decades, that people have defined themselves more by how and what they consume and less by how and what they produce; is Google perhaps the first corporation to follow this trend?
That last question is sort of a curiosity, but I think a serious issue for Google is this: as the people of the world, those people you're making information accessible to and useful for, are your products and not your customers, how do you manage conflicts of interests between your mission and your business? Obviously there have been many companies with similar models, but few that have remained public darlings for long. Consider the media's pandering, fear-mongering, and lack of substance — how seriously can we take its claims to journalistic responsibility? How does Google avoid becoming Facebook? Is it just that it doesn't have Mark Zuckerberg?
I think ultimately that's all it is. Google's people, right now, are more moral than Facebook's, and the company makes enough money that it can afford to be. It's similar to self-imposed limits of power in government: they're as good as the people (self-)imposing them. So as with just about any entity — governmental, corporate, social — the principles just don't matter. No principle can keep Google in check. Only people.