Because losing their job and being charged with a felony for breaking a TS clearance is totally worth doing that for you. The NSA isn't a startup in stealthmode. I can guarantee you that some HNers know NSAers, and no doubt many HNers are NSAers, but there are very strong reasons why they're not participating in this dialogue.
Read the Wikileaks documents. Triviality. Small-thinking. Nonstrategic low-value goals being pursued. The diplomatic equivalent of spam. Read it, and you will be convinced there is no bear in the woods, no boogie man under your bed that the NSA can't tell you about.
And that last 0.0001%? We can afford that price for freedom. Total transparency won't hurt America at all.
I don't like the fact that they're doing it, but presuming that they should operate in total transparency just so that the silicon valley "proper thinkers" won't assume the worst is fairly naive, IMO. They believe they're fighting a critical intelligence war, and secrecy is an integral and necessary part of that battle.
I wouldn't work there, but I respect the people who do, both for their technical ability and for their patriotism. (I may not agree, but I can respect.) In particular, they're making significant individual sacrifices in order to do the work they do. It's not the same sacrifice as doing IED patrol in Afghanistan, but anyone doing high level crypto for NSA could likely make more money and have a cushier life in the private sector.
Where does the funding come from? From the tax payers. Who gets spied on? Everyone and their dog. So yeah, they're making a sacrifice, but even bigger sacrifices are forced on just about everyone else.
This would be a much more sensible argument if they weren't going around outright coercing Silicon Valley's tech companies into becoming their tools.
If the NSA wants to spy on everyone, they should do it the hard way!
That's very unlikely to happen, because it's all classified and secret or top secret or whatever.
There are a few interviews around.
Here's an ex-director (He stopped being director in 1978) http://www.bbc.co.uk/programmes/b039vhp0 - this is the first time he speaks about his time at GCHQ
Here's a radio documentary from 2010. http://www.bbc.co.uk/programmes/p007fqc4
I have written to the BBC and asked what conditions the agencies laid-down but I did not receive a reply.
I'm certainly not a fan of his ideology, but he gives an insight from someone who came from the NSA and is supportive of the executive branch's behavior.
My only objection to the NSA stuff is not the collection of information, but the asymmetry. Snooping on all my emails isn't wrong because email should be private, it's wrong because you have power over me by knowing my email without me knowing yours. Fortunately, things like facebook and twitter acclimatizing people to publishing everything about their lives which will eventually eliminate this asymmetry.
I totally agree that people have varying beliefs on this stuff and for some this might be just as noble as any other way of serving their country.