"I can see how you would get that impression if you only read the Tweet I highlighted, but Greenwald was responding to a conversation questioning if Snowden's disclosures were in fact whistleblowin"
Hm, I read a bit of that conversation before, but didn't got that impression. I will read deeper into.
" to gain favor with the US government or intelligence communities he would have to be leaking something that puts them in a positive light."
Or ... he choosed not to leak some other dark secrets, he learned about. But still has them as a life insurance ...
"That isn't the way the law works."
Erm, first of all, I thought we were talking about your opinion on the matter and afaik, you are not the law.
And secondly, yes you can indeed negate crimes, if you did something good ... if the "crimes" were the only way to do the good.
That's the whole concept of whistleblowing - it is a crime to reveal secrets, if you agreed not to. But you are allowed if you show, that the persons you work for, were (at least partial) criminal in the first place.
And this is what Snowden did.
And if he later after revealing, was left of no choice, than to go to the russians - because nobody in the US-Government said, "ah good, you showed the people the truth, now come home, we work things out for the better" - I could understand that, to give then the russians minor secrets, if forced to. What else could he have done? But this is only speculation and far from being a fact. And I don't think, the russians did pushed him in such a way, because of public opinion ...