Alright. First of all, let me say I am not touching on Assange's current prosecution, the theories that it is probably being pushed by the U.S. government, or anything else.
I am speaking purely about the debate over the morality, and in particular, the legality, of WikiLeaks and the newspapers it has provided information to, publishing "secret" information.
I am not a lawyer. But I once had plans to become a journalist, and as such, we studied issues related to this case. In general, there are three freedoms recognized as relevant to the freedom of press.
First, the right to access. This is the right of the press to access key information.
Second, the right of protecting sources. This is the right to maintain sources' anonymity.
Third, the right to publish.
Coincidentally, these three have been listed here in reverse order of their traditional support from the U.S. courts. Let's break down each issue as it is relevant to Assange and WikiLeaks.
The right to access. Unquestionably, the courts have maintained that in certain cases regarding a public interest, or an individual's rights, the government has right to limit press access to information. For instance, some states do not allow cameras in court rooms. The U.S. government can control "imbeded" journalists. The federal government can classify documents (like those released by WikiLeaks) and attempt to keep them from the public eye.
Second, the right of protection. Many states partially protect this, but many do not. There is also no federal shield law, meaning there is no "journalistic privilege" in a Federal court. Also, in most states, the right to shield a source is protected in a bench or jury trial, but not in a grand jury deposition. This means the federal government could, in theory, prosecute the individuals who illegally gave Assange information and expect him, even compel him, to testify against them.
Third, the right to publish. This is the most protected right involved in freedom of press. In short, a media outlet has a right to publish any information that they have access to, assuming that they did not break the law in obtaining the information. For instance, courts have ruled that a newspaper could publish both a rape victim's name and a juvenile offender's name (both protected by law) because a reporter got access to the information through a lawful viewing of court records. A court also allowed a newspaper to publish photographs from an execution, although photographic equipment was banned from the execution viewing room. The act of taking the pictures was illegal. The act of publishing the pictures once they fell into possession of the newspaper, was not.
In short, the government has every right to force Julian Assange to give up his sources. They also have every right to discipline those sources, both as government employees violating the terms of their employment, as well as possibly as traitors and/or spies. If Assange (a former hacker) is found to have stolen the information through illegal methods, it would be a different story. The problem with this is that because Assange is not within U.S. borders, without accusing him of having violated a serious law, he cannot be compelled to answer questions about his sources.
At the end of the day, though, Assange and the publications he worked with have published information that they obtained legally (it was given to them). They should not be prosecuted. The lying, treasonous government employees who leaked the files should.