International spying on your allies, including corporate espionage against countries like Germany. That angered your allies much more than it endangered them. Whistleblowers like Snowden are the mechanism that keeps that spying from happening in the first place.

Edit -- And yes, this harmed America by undermining the trust that those countries had in it. But to be clear, it wasn't Snowden's disclosure that broke that trust, it was the spying. It's hubris to think that if not for Snowden it would never have been discovered, and the longer it went on, the more harm that would have been done between America and its allies when it eventually got found out. So by revealing it early, Snowden really minimized the damage, rather than causing it.