One sentence from the piece. "If federal security agencies can’t do vast data sweeps, they will inevitably revert to the older, more intrusive eavesdropping methods."
1. Eavesdropping does not disappear when vast data sweeps are allowed.
2. The problem with secret vast data sweeps is that they are secret and the efficiency cannot be questioned by the public. Even if the result of the sweeps induce more eavesdropping and wasting even more resources.
He doesn't exactly question that the data sweeps are accurate or not, he just assumes that they are. After a little exposure to machine learning, data mining and statistics he might question them a little more.