Ah, but that's the issue. As currently constructed, the espionage act cannot be challenged in court.
Assange would want to argue that he isn't a spy, but a whistleblower. The argument would be that he willingly broke a law in order to expose more illegal behavior by the government. In order to make that argument, he has to be allowed to talk about what the government does.
Under the espionage act, though, the government can say that the details of their activities are classified, and therefore are not admissable evidence in a public trial. Therefore, their guilt cannot be proven because any claim of illegal behavior could not be backed by evidence.
This is plainly false. The judge is the one who decides if the actions of the government bare relevant. If the judge believes they are, they will be admitted, and parts of the trial will be closed, but other parts will remain open.
I would urge you to do research to confirm your assertion here. What I described is not a fringe view, it's literally a summary of the Criticism section in the Wikipedia entry for the law in question:
No one is saying that civil disobedience should be consequence-less. We’re arguing over the legality of the laws one would be breaking and whether they’re just.
Assange would want to argue that he isn't a spy, but a whistleblower. The argument would be that he willingly broke a law in order to expose more illegal behavior by the government. In order to make that argument, he has to be allowed to talk about what the government does.
Under the espionage act, though, the government can say that the details of their activities are classified, and therefore are not admissable evidence in a public trial. Therefore, their guilt cannot be proven because any claim of illegal behavior could not be backed by evidence.