Currently the NSA is able to harvest mountains of data. It's legal because the governnment isn't "actively" using it.
The government is not doing this for shits and giggles.
Eventually we will hear of stories in the news of warrants being constantly issued for this phone data to seal convictions. The tin foil hat side envisions a scenario comparable to"The Handmaid's Tale" in that many laws are passed at once and this is the final nail to convictions we currently find unimaginable.