NSA, FBI and other alphabet agencies were unable to provide even one single case where all this surveillance helped prevent an attack.
You haven't been paying attention. Every few weeks there's a story about an arrest of a group of bomb makers or other terrorists - usually with a batch of defective chemicals supplied by a gov't planted agent.
This liberal/conservative dichotomy seems to be precisely what keeps American politics stuck in a never ending rut.
I bet you think a woman can be partially pregnant.
I have had a doctor make a mistake on me, and it cost me weeks of pain (fortunately, no permanent damage.) The pain was entirely unnecessary; the doctor was ignorant.
Doctors are not omniscient, and by living in my body I can be quite familiar with it. Blindly following a doctor's advice can be as destructive as never following it.
Look at how maps changed over the course of the 20th century. Countries defeated in war by the U.S. became countries again; countries defeated by the USSR became either part of the USSR or occupied by the USSR military, and stayed that way until the end of the cold war.
The threat of totalitarian communism was and is real, and the "threat" from western democracies is a hallucination from loons like you.
What you said, and more. People born before 1950 should remember that there were real spies stealing real military secrets that could have, and in some cases probably did, result in American deaths. Snowden appears not to have been entirely able to distinguish that sort of secret material from safer stuff.
Government domestic spying has become egregious, and by exposing that in a manner that stays in the news, Snowden has advanced freedom. Whether the balance of the effect of his actions will be positive will probably never be known.
It is beyond question that what he did was dishonest, in violation of legally binding agreements he made with his employers, and in a narrow sense treasonous. Let's hope the net result is better government behavior, not a doubling down on domestic spying.