All of this came about because for the first time since 1812 the war came from outside to inside the US, and it wasn't brought here by an organized nation "over there", it was brought by fanatical, irrational ideas that unlike all previous wars we were involved with don't need an industrial base or a geographical location, or in some ways even communication between its proponents to operate- the soldiers in this war have no need for an army, a navy, an air force; IEDs, suicide-bound zealots wearing explosive vests, pressure cookers full of explosives in a backpack are their weapons, along with compromising our assets like airliners and rental trucks. Paraphrasing Pogo with one word added" "We have seen the enemy and he is (among) us". The mentality that is stalled at the concept that war is only nations violently (or threatening violence) opposing each other, enemies being full-on industrial nations equipped as we are to wage war on a grand scale at specific, obvious locations (such as east Germany or the Pacific or western Europe) is in dangerous error.
What is the US to do about this threat? If the guy next door has terrorist intentions, how are we to be protected from his attack? If all the means and methods the government has to find and thwart assassins such as Dzhokhar and Tamerlan Tsarnaev or Timothy McVeigh or Mohamed Atta are known, then we have no effective defenses. Who knows what might have been done had a government agency saw the words "Ammonium nitrate" "nitromethane" and "Waco" in an email and looked into who sent it.
Thanks to Snowden, one of the most effective means of finding such threats was revealed to the public, thereby diminishing its effectiveness; the clamor of the public who thought of nothing but their opinion that their rights were being abused added to its neutralization.
I don't mind if the government wants to read my emails any more than I mind a police car behind me in traffic. I have nothing to hide, I'm doing nothing that threatens anybody or breaks any laws. If they choose to investigate me they will soon find that out. And if such surveillance would lessen the risk of a shopping center blowing up or another building being leveled, I'm OK with it.
I don't have a fundamental distrust of the government, I look to it to do whatever is necessary to protect us, within the limits of the premise that ours is a government "of the people, by the people, for the people". As I see it if we are constrained by our ideals at the expense of what's practical in the service of our people, we are vulnerable.