Never under estimate the predictability of stupidity.
Someone already mentioned in here, if a newspaper wants to go ahead and do some proper investigative reporting and bring some real dirt and details into it then it might be worth it. But what we have here is the parrot media that is slanted, biased and pushing the governments agenda or deflecting from its failures.
These programs are there to create and manipulate, blackmail and coerce, commit industrial espionage, spy and profile, steal governments secrets, suppress political dissent and popular protest before it happens. And maybe catch a few poor terrorists who need our help.
The sender and receiver of the encrypted email must know the cipher key as you mentioned. Maybe they will flag you and try to obtain that cipher key. No they do not like encryption. Some are so good they cannot be cracked.
The more we look at the second leaked program Boundless Informant the less it looks like a back door. It more resembles a sluice gate that opens onsite servers at Google data centers and flows the "valued" data in to the NSA SIGNIT database. It has to be in real time and is all collected. eg. Google flagged works, get a visit.