Back in the 1950s, MI6 continued to back Kim Philby, despite loads of evidence that he had been a Soviet spy for some long time.
That might have been the old boys' club (which was practically the definition of MI6 at that time) or an inability to admit they had gotten him so badly wrong.
The NSA has reacted quite differently to Edward Snowden, but a large group of people, including reporters and editors, feel strongly that he is in the right.
We have very little information about Snowden's activities in late 2011 and early 2012, as he was leading up to going public with the NSA's information. I am bothered by interviews with Snowden through email. How did James Risen know it was Snowden he was talking to? And in-person interviews are only a little better. In both cases, the reporters have done little beyond conveying Snowden's words to us. Usually reporting requires confirmation by other parties.
Much of what Snowden says is not subject to verification, although even his reports of what he was thinking could be checked with his former co-workers and friends. Very little of that appears in the news stories, however.
It's likely that the NSA has told employees not to speak about Snowden. They are doing their own investigation and would prefer that not too much of it leak. The FBI is probably also investigating.
Many of the stories based on materials provided by Snowden have the same problem: little actual support for the interpretations and allegations is provided. Sometimes documents are provided, but slide presentations are particularly unreliable, and other documents lack context. Many of the documents are from four or five years ago. The NSA is unlikely to say "No, here is the truth about our classified programs." So the reporters are essentially saying "Trust us."
The fact that the documents Snowden and his reporters have released go so far beyond his stated purpose of provoking a discussion of privacy raises questions as to his motive.
Reporters seem to love leaks, though, and certainly their jobs are easier with them. So I would ask the reporters and editors who are supporting Snowden to consider if they might not be in the position that MI6 took with regard to Kim Philby. He's our guy. He must be right.
Figuring out this whistleblower/leaker/espionage thing is really hard. That's the point of espionage, of course, to confuse these things. It's still not clear where Philip Agee lands on that spectrum, and we know much less about Edward Snowden.