Snowden/Manning also found themselves in a position to use more leverage, and in those cases it's a separate moral question about whether they chose wisely to take that opportunity or not. (FWIW, I've never seen anyone giving them carte blanche to do whatever they would like with the info they accessed -- that's a straw man).

You can't just bypass that discussion by saying "they're allowed to vote, that should be enough for anyone".

No, it's not a separate moral question. It's the crux of the discussion. The entire spectrum of possible actions was open to them. "Do nothing" vs. "Do something" isn't a very interesting distinction: "Something" might have been to quit their respective jobs as soon as possible, or post snarky comments about the evils of the U.S. government under a pseudonym on reddit, or flee to Hong Kong, or blow up a building where they worked...

Nobody elected Ed Snowden or Chelsea Manning. In fact, the people we did elect put trust in Snowden and Manning to preserve certain secrets. Both proceeded to release not just secrets that exposed malfeasance, but the sorts of things (NSA overseas operations, diplomatic cables) that, by and large, our (inevitably imperfect) democracy has decided are peachy keen. Criticizing that indiscretion isn't giving in to "the system", it's acknowledging that "the system" is one we have built together, and there are certain aspects of its operation that are not subject to the whims or passions of people who had previously sworn to uphold it.

The press is a hugely important part of democracy, because it's their job (in theory, anyway) to keep the populace informed of what their government is actually doing in their names, vs. what they claim to be doing.

If the government is lying about what they're doing (and doing things that are contrary to principals they're pretending to uphold), whistleblowers are necessary.

I agree that if you live in a democracy, you're going to sometimes disagree with policies the majority things are fine. If I think legal abortion is evil but politicians who explicitly support it are elected, I should not "exert more leverage" by threatening to detonate a dirty bomb if the laws are not changed in 72 hours.

Whistleblowing is different -- it's the act of revealing information that was intentionally hidden from the public. Certainly, it may be breaking laws (and the laws may in general be justified!); that doesn't mean the whistleblower's decision is automatically wrong, or that they're cheating the normal democratic process. On the contrary, in most examples they're exposing others who are cheating (by hiding pertinent information from voters, thus affecting their votes).

Your (inevitably imperfect) democracy has also decided the facts of malfeasance to be peachy keen, so that's hardly a justification.