It's about conspiracy, not press freedom. Yes, we should strongly protect the press's right to publish virtually whatever it wants. That's not in question.
What is in question is can the press continue to be the "press" when it conspires with others to break US law? Assange is alleged to have been in contact with Manning (either directly or through intermediaries), BEFORE any of the data breaches occurred. And it's possible that Assange or his colleagues provided material support to Manning in his criminal act. IOW, he was an accomplice before an after the fact.
That is wholly different from the NY Times recieving anonymous classified materials in the mail, and then publishing them. Or, speaking whistleblowers who may then disclose information that they did not come to learn of by theft. Manning stole these documents (allegedly) and Assange very well may have helped him.
Just like the attorney-client privilege doesn't shield lawyers from criminal conspiracy charges if they knowingly engage in criminal activity with a client, the reporter-shield law shouldn't inoculate the press when they knowingly engage in criminal activity.
I certainly agree with all that, and was unaware there were claims he conspired to acquire the information.
I presume you are aware that a great deal of “investigative journalism” conspires to break various laws all the time, certainly after the fact of the crime if not before. Fraud, theft, etc. In fact, without the law breaking it would be real difficult to do investigative journalism.
The way it often works is: “whistle-blower” who works for corporation contacts member of press, tells what he has got, journalist works with him to figure out what information will work best. WB trots off and steals the relevant data, provides it to journalist who publishes it. Sounds like conspiracy and accessory before and after the fact to me, and except for the national security connection exactly what Wikileaks is accused of.