If people wanted control over where they’re aggregated, I supposed something equivalent to a robots.txt file could be invented. But it’s not sporting to refuse to be counted. And there’s no point in invoking privacy concerns—face it, if the NSA wants to read your tweets, they’ll find a way.
As a user, consider how much control and security you really want over your online identity. How do you feel about leasing an identity from a web brand? Unsure about the benefits of owning your own?
These are so different from what people who are not total Web-heads mean by “privacy” and “control” that it might as well be software from another planet.