So by definition, you can only whistleblow if the government (or company) is doing ILLEGAL (and often IMMORAL) things. So you may not find many people on HN who are too interested in arguing about the downsides of whisteblowing; it'd almost be like asking what the upsides of spousal abuse are.
Essentially, yes, but the difference is with the sad fact that a certain percentage of people, unfortunately, have a will to bow before power in certain ways, i.e. enter nationalism. In other words, it's more like arguing about the upsides of torture, or the upsides of unjustified wars--those are atrocities committed by your government, not your neighbour. These I have seen discussed with (unbelievable) earnest on cable news, such as CNN.(1)
1 - https://theintercept.com/2016/09/09/wolf-blitzer-is-worried-...
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.
Legal channels were shown to be utterly ineffective in these matters, accomplishing nothing but drawing retribution against the would-be whistleblower: http://www.commondreams.org/news/2016/12/15/nsa-inspector-wh...
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.