> revealed information that has little public interest
This is false, in a very strict sense; after almost 3 years, the entire world is still debating about his work - if this is not "public interest", what is?
> isn't illegal activity
> you can't simply say the good outweighed the bad
This is actually a serious problem of it. Actually, under a certain interpretation, this is the radical problem - lack of accountability. The Clappers of the situation can do/say whatever they want, and get away with it.
If you put this in a political context where if you make a documentary about Iraq you go in the government dissidents watchlist [Poitras], you see the direction towards authoritarian themes; in my book, this is as bad as it gets.
> has the right to release information they morally object without any legal repercussions.
This is misinformed; Snowden said he would have come back in his home country, if there had been a fair trial.
Whether this is true of false, everybody knows, that the alternative to "without any legal repercussions" is being crushed by some draconian laws of the early 20th century.
> They instead grabbed everything they could get their hands on in the off chance it was something they were looking for. Isn't that the exact problem we have with mass surveillance in the first place?
If we put aside rhetoric, then definitely are very different problems.
There are several reasons why the Mannings/Snowdens could actually keep releasing documentation (including survival, or keeping the public interested, or in unrealistic worst case, frivolousness, arrogance or else), which are radically different from the reason of mass surveillance, which boils down to power.