There was a foreignpolicy.com article on HN recently that boils it down succintly. Snowden's disclosures severely damaged the American advantage of hypocrisy.

There was a foreignpolicy.com article on HN recently that boils it down succintly. Snowden's disclosures severely damaged the American advantage of hypocrisy. By being able to publicly take the high ground on an issue, while covertly doing the dirty stuff behind the scenes, we were able to enjoy the advantages of both strategies. With that strategy damaged, it will make it far more difficult to achieve our diplomatic goals on multiple fronts. Maybe Snowden was purposefully helping the Chinese, maybe he wasn't. Either way, the NSA was doing a lot of stuff it should not have been doing. Had they not been violating the constitution with their activities, there would've been nothing to report. Not to mention the fact that if they had proper internal access control, Snowden would not have been able to get away with as much information as he did. If Snowden were a Chinese spy, well, the NSA did a shit job of preventing espionage. And who's to say there aren't foreign agents in the NSA right now, stealing information?