If a single foreign national is rounded up and put in jail because of a leaked cable, this entire, anarchic exercise in "freedom" stands as a human disaster. Assange is a criminal. He's the one who should be in jail.
–Joe Klein, Swampland (12/1/10)
Actually, Julian Assange didn't leak anything–he can't, because he didn't have access to classified documents. Someone (or someones) who did have such access leaked those documents to Assange's WikiLeaks, which, as a journalistic organization, made them available to the world, both directly and through other media partners.
This distinction, which is widely ignored in commentary on WikiLeaks, is actually quite important, because the ethical obligations of a government official with a security clearance are quite different from those of a media outlet. An official makes a promise to protect classified information, and should break that promise only when the duty to keep one's promises is outweighed by the public interest in disclosing wrongdoing. Journalists, on the other hand, are not in the business of protecting secrets, and should have a general presumption in favor of informing the public unless disclosure would cause specific foreseeable harms. The two ethical situations are pretty much opposite.
To treat Assange as a leaker when he is, in fact, a journalist is not only morally confusing, it's quite dangerous to journalists in general. If the government can declare Assange to be spy or a terrorist because he's published classified documents he's received, every investigative journalist who does the same thing is in deep trouble.