That's not what they're trying to prosecute him for. They're prosecuting him for conspiracy to break into DoD computers. That's kind of similar, but it's not the same thing.
You're correct, but it's not immediately clear to me what it means to be part of such a conspiracy.
Would simply receiving classified information from Chelsea Manning count? (Probably not, I would guess.)
What about receiving classified information and then remarking "Wow, this is great stuff! I'm going to pass this information on to prominent news organizations through my website called Wikileaks. You don't have more that you could send me, do you?" Would this count as conspiracy if his remark lead to Manning obtaining more information in an illegal manner? It seems that something along these lines may have happened.
It seems to me that Assange should only be prosecuted if he broke into DoD computers himself. It doesn't appear that such an event occurred. I believe that discourse between a journalist and a source (or any two civillians, for that matter) is protected by the 1st Amendment. Thus, encouraging Manning to hack government computers, or even describing to her how to hack government computers[1], should both be protected by the 1st Amendment.
[1] Perhaps this opinion is controversial. Allow me to lay out an example:
Source: "I've sent you all the info I have! Everything else is password-protected."
Reporter: "The password isn't 'password123', is it?"
Source: "Hey, that worked! Let me send you some more stuff to help with your expose."
In this case, or even if the reporter suggested something more technically advanced like "Hey, look up sql injection on Wikipedia," I believe that the reporter's speech is protected by the 1st Amendment. (The source's activities are almost certainly illegal, but that doesn't answer the question of whether they should be prosecuted for them).
I suspect that if someone did source research by breaking the security of your computer, you would want them prosecuted, too. Journalists can't be persecuted for what they write, but they're not above the law.
Sure, in the same sense that the same description could apply to torturing someone with relevant knowledge.
Freedom of the press is the right to publish, not an exemption from all criminal law so long as the object of the crime is acquisition of material for publication.
This actually seems like great news for journalists. The fact that this is the only charge implies that prosecutors have decided that wikileaks’ core activity of publishing classified information obtained by others was actually legal.
The fact that assisting someone to break into a DoD computer turns out to be illegal probably shouldn’t surprise anyone. If someone asked for your help breaking into a DoD computer would you say “oh sure, that sounds like a perfectly legal thing that can’t possibly get me into trouble”?
I wouldn't underestimate the US. They could be laying this nice, comfy-looking trap to ease the extradition process from UK. Then once on US soil, the real charges are unveiled.