Senator Frank Church said of NSA technology in 1975 words which are more urgent today: "That capability at any time could be turned around on the American people and no American would have any privacy left. There would be no place to hide. If this government ever became a tyranny, the technological capacity that the intelligence community has given the government could enable it to impose total tyranny. There would be no way to fight back, because the most careful effort to combine together in resistance to the government, no matter how privately it was done, is within the reach of the government to know. Such is the capacity of this technology."
Money quote.