Fate gets a lot of mileage out of who we love and who we hate. I would hazard that association is the most fundamental and powerful way we ordinary people change the world.
Knowledge is control. Total knowledge is total control. It is control not just through truth, but also though falsehood. He who has all the information, the secret evidence, has an ability to lie and sculpt more effective half-truths and deceptively persuasive out of context conversational atrocities.
People are notoriously apt to manipulate the truth because doing so is simply in their self-interest. For some, particularly among the powerful, this comes as naturally as breathing.
Taking these points in combination, allowing secret government entities access to mega-communications-metadata might not be such a brilliant idea. Omniscience of metadata (information regarding our personal relationships) is omnipotence over our fate.
Is there anyone in any government we rationally trust with that magnitude of power?
Metadata, by plotting our interpersonal affairs, has a capacity to pierce the heart of who we are, the source of our greatest power and greatest weakness, our associations.
In addition to revealing the most basic truth of our lives, meta data has a capacity to generate numerous and very persuasive false positives for projection onto our lives.
Consider me, an ordinary bloke, a nobody who knows nobody who is really anybody. Yet, having explored just a few degrees of separation, I find myself related by fairly short chains of connection to a dizzying array of people. Attempting to catalog these connections, I have found no end to them, as each link leads to a thousand more. Let's take the Dalai Lama, for example. I lost count years ago of the number of links I have to him via short-chain connections through other people. An examination of my metadata would strongly implicate me as a Dalai Lama conspirator, but that metadata would be misleading. I've never even met the man unless you count listening to him speak to a throng of tens of thousands of other souls.
A deep look into a person's metadata ocean produces a shifting fun house mirror of refractions, mirages of light, exploitable by a powerful entity wanting to portray the individual in any true or false light it found convenient. Once you have a large enough sea of signs, you can pick and choose what ever bits you like to make a person out to be whatever you want them to seem to be. Whoever controls the information has the power to sculpt the perception of reality however he might wish, especially when evidence that contradicts the chosen message can be kept entirely secret even from legal proceedings and lawmakers.
It isn't that we might simply be kept in the dark. Rather, we will inevitably come to see people, the world, and its relevant political issues in any variety of false lights that suit the interests of power. We will not be able to discern when we are being duped as easily as one could discover whether one were merely being kept in the dark. What we are susceptible to is a radiant light of darkness, which is far worse than simply an absence of light.