Also Snowden was certainly aware of the fates of previous intelligence leakers like Thomas Drake[0] and William Binney[1] and others who tried to blow the whistle through the proper channels, only for nothing to happen.
[0]http://www.smithsonianmag.com/history/leaks-and-the-law-the-...
[1]http://www.computerweekly.com/feature/Interview-the-original...
Even if not, Thomas Drake is a prime example of what happened to whistleblowers at the NSA - and Drake was an employee, who (theoretically) had access to greater whistleblower protections than Snowden would have had as a contractor[2].
So yes, I'm saying that it's very easy to believe that Snowden took a look at what happened to NSA whistleblowers and took a different path.
[1]: from the POGO story: "POGO has been told that mention of the finding will appear in a semiannual report (SAR) of the Intelligence Community IG (ICIG) that should be released in the near future. It makes brief mention of the case without citing Ellard by name." So we may get some more information about timeframes at some point.
[2]: From TechDirt (https://www.techdirt.com/articles/20161215/16354636293/snowd...) today: "The new directive created better protections but would have done nothing to aid Snowden in taking his complaints to the proper channels because he was only a government contractor, not an actual government employee."