The trouble is that in most of the recent prominent government "whistleblowing" cases (Snowden, Manning, the other one I forget) there's a great deal of disagreement on the legality of what has been exposed. The issue is that an individual sets himself up as judge and jury on the subject of complicated legal matters which he might not fully understand.
I will say that both Snowden and Manning went well into the territory of leaking stuff that wasn't illegal in addition to stuff that was at least debatable.
And how many judges were consulted on wether the spying was legal, let alone got to rule on it? How carefully chosen were they? And how legitimate are such secret trials? You accuse whistleblowers of playing judge and jury for merely revealing what the government is -doing-.
Finally, the entire appeal to 'legal matters' is misguided - whistleblowing is done when someone feels something is -morally- wrong, regardless of what the law, written by the government and interpreted in secret, says.
I will say that both Snowden and Manning went well into the territory of leaking stuff that wasn't illegal in addition to stuff that was at least debatable.