Your question is obviously irrelevant. Whether or not they
have flagrantly abused the power is irrelevant.
What is relevant is whether or not they could, how easy it would be to do so, how damaging it could be, and what protections we would have once they have done so. This is the threat presented by internet monopolies and their fetish for violating our privacy.
Also consider that no company has managed to stay on top indefinitely. Once their growth slows, and they become desperate to appease shareholders, what won't they do to make that happen?
Long after fads have changed, supposed benevolent coding wunderkinds have moved on, the troves of data will still be there, ripe for the MBA's, the lawyers, the mitt romney's, god knows who, to leverage.
The argument "they've been nice about it so far, so why shouldn't we keep doing it?" is a fucking joke.