I tend to believe Snowden. I believe that he damaged his own life in order to inform the American public of citizen-spying that Edward found to be immoral and unethical. His releases were to news media for public enlightenment, not to private sources for financial gain. I simply don't see any other major motivations at play.
https://en.wikipedia.org/wiki/Edward_Snowden The Department of Defense alleges that he copied 1.9 million documents. He only made 10,000 of those public.
Snowden quotes before the publication of information: "I understand that I will be made to suffer for my actions, and that the return of this information to the public marks my end."
"All I can say right now is the US government is not going to be able to cover this up by jailing or murdering me. Truth is coming, and it cannot be stopped."
"I have no intention of hiding who I am because I know I have done nothing wrong."
"I don't want to live in a society that does these sort of things [surveillance on its citizens]... I do not want to live in a world where everything I do and say is recorded... My sole motive is to inform the public as to that which is done in their name and that which is done against them."
And after:
"For me, in terms of personal satisfaction, the mission's already accomplished. I already won. As soon as the journalists were able to work, everything that I had been trying to do was validated. Because, remember, I didn't want to change society. I wanted to give society a chance to determine if it should change itself. All I wanted was for the public to be able to have a say in how they are governed."
"I acted on my belief that the NSA's mass surveillance programs would not withstand a constitutional challenge, and that the American public deserved a chance to see these issues determined by open courts."
"There's no saving an intelligence community that believes it can lie to the public and the legislators who need to be able to trust it and regulate its actions. Seeing that really meant for me there was no going back. Beyond that, it was the creeping realization that no one else was going to do this. The public had a right to know about these programs."