Read all of Cassidy but here's an excerpt:
So what is Snowden’s real crime? Like Ellsberg, Vanunu, and Bradley Manning before him, he uncovered questionable activities that those in power would rather have kept secret. That’s the valuable role that whistle-blowers play in a free society, and it’s one that, in each individual case, should be weighed against the breach of trust they commit, and the potential harm their revelations can cause. In some instances, conceivably, the interests of the state should prevail. Here, though, the scales are clearly tipped in Snowden’s favor.
I’ll leave the last word to Ellsberg, who, for revealing to the world that that Pentagon knew early on that the war in Vietnam was unwinnable, was described in some quarters as a communist and a traitor: “Snowden did what he did because he recognised the NSA’s surveillance programs for what they are: dangerous, unconstitutional activity. This wholesale invasion of Americans’ and foreign citizens’ privacy does not contribute to our security; it puts in danger the very liberties we’re trying to protect.”