I don't think it's as black and white as that. Maybe the NSA spying on some overseas entities isn't strictly illegal. But to understand the bigger picture of their all-encompassing reach and sheer pervasiveness better emphasises their wrongdoings on US soil because it helps explain why the NSA's general mentalities of 'we have the right to collect ALL of the information' and 'we are above the law' exist.

Am I saying I think it's outright justified? No, because I'm honestly not sure. I am however sure that it's not as black and white as 'legal' vs 'illegal' when it comes to whistleblowing because the extra infromation helps us establish a context and understand a sense of scale of the wrongdoing, for example.

edit: Here's an example: It's probably not illegal that the 'official' estimates of civilian deaths in the Iraq war were likely far lower than the reality. Assume for the sake of discussion that this was intentional. Having a better understanding the more realistic magnitude of civilian deaths helps the public understand the realities of such wars and helps them make more informed decisions on whether they're comfortable with the actions of their government. It changes the context of the Iraq war and may go from 'we were justified in doing it' to 'it wasn't worth it' for some of the voting public.