*I* say, he talks of hidden mechanisms, he requires other people make some moral determination about those mechanisms, and he has an opinion already that he thinks mandated pushing the moral question out to everyone else. *And* he appears to know a lot of other things. That wealth of hidden background would ordinarily appear as ponderous conspiracy theory, but here apparently it's okay because NSA.

Again: it's an exposé, not a conspiracy theory. He isn't hiding anything; he's leaking it. He isn't blowing up his part and lecturing with the grandiose pomposity of the average INTJ, he's just stating the facts. Obviously, he has an opinion, he's just not arrogant enough to believe it's the only one that counts.
The public is supposed to decide something. I haven't heard or read everything he's said, but does he ever talk about principles being violated?
"I don't want to live in a society that does these sorts of things"
It's common for INTPs to be more certain about what they don't want/ aren't prepared to tolerate, than what they do. He knows that he doesn't want to live in a society full of hypocrites and slaves, but he doesn't necessarily have an overarching vision for some sublime Utopia either. Or put another way, he defines Utopia by what it doesn't contain, rather that what it does.
The INTJ stipulates the world he wants to live in; the INTP the world he does not.
Ni supplies a singular "perfect" vision, and Te the means to accomplish it. There is a narrowness of focus and rigidity of purpose.
Ne supplies endless possible states and Ti tests and eliminates those that won't work because they violate some core principle or are inconsistent in some other way. Negative capability:-
" the ability to tolerate the pain and confusion of not knowing, rather than imposing ready-made or omnipotent certainties upon an ambiguous situation "
Snowden has this in spades. It informs his political ideals as well as his personal life choices. It's anti-J. (Or P, more concisely. )
He recognises that the NSA's method of snooping is both "the most efficient" and an "abuse". Isn't that like, an oxymoron for an INTJ? Je is all about ends justifying means.
Snowden doesn't trust authority - not even his own. The fact that he was authorised to spy on the President on the flimsiest of pretexts, frightened him. Whoever said "Power corrupts; absolute power corrupts absolutely" - I'm thinking it wasn't an NTJ.
Ed Snowden said:
"No one can meaningfully oppose them. But at the same time you have to make a determination about what's important to you."
"You could shut down the surveillance system in an afternoon, but that's not my intention."
"If you can live unfreely [sic], but comfortably (and I think many people can - it's human nature)..."
"But if you realise that that's the world you helped create, and it's only going to get worse with the next generation's capability to extend this Architecture of Oppression....then you realise you're prepared to accept any risk, and it doesn't matter what the outcome is, so long as the public gets to makes its own decision."
Could he be
less INTJ?
The INTP is as reluctant to impose his will on others as he is to have others impose their will on him. Both attitudes inform Snowden's actions. He can simultaneously believe/fear that his actions will have no lasting legacy, yet still be convinced it's the right thing to do: ends are largely irrelevant.
He doesn't press his vision upon the world, because he recognises that his is only one perspective (Pe) all the while being convinced of its subjective rightness (Ji). He distinguishes between moral absolutes and technical facts. He collects and presents those facts and allows others to draw their own conclusions without trying to get in the way of that process any more than is necessary (also known as Informative vs Directive). His own conclusions coupled with his disposition create a moral imperative which has dictated the course of the rest of his life, but he doesn't actively intervene to destroy the system he despises (as you suggest an INTJ would). He does however, subvert it. He allows a more informed public to decide their own fate, while his lack of faith in human nature guarantees his retreat, rather than than trust his own fate to others.
Come now. You know it makes sense. You're infatuated with an INTP. It happens.
We are kind of wonderful.