Actually, no, US newspapers don't STEAL information, which is what he's being charged with. If you get it from another source and you weren't part of acquiring it, you cannot be legally responsible for it (it's not like receiving stolen property). But the governments case is that in statements to manning is that he was active in ACQUIRING the information. Therefore he can be held criminally liable. Now whether those statements are really enough to hold up in court are a huge issue, but it won't matter because one they get him here they can add on a ton of charges -- perjury, conspiracy, and whatever national security rules they want. But your point #1 is not valid in that if US newspapers did ever steal information they could be held criminally liable (they don't).
I’m no international law expert, but wouldn’t the UK demand that the US disclose in advance everything they plan to charge him with?
Otherwise, couldn’t he argue in the UK that his rights might be violated by the extradition, in the event that the US charges him with something that isn’t considered a crime in the UK?
Assange, and his lawyers, made all kinds of arguments and appealed his extradition to Sweden all the way to the High Court and lost. He hasn't actually had any court time related to the U.S. extradition because he fled. I would assume that if he had a decent chance of winning on the merits for the U.S. extradition, he wouldn't have spent 7 years hiding in a cupboard.
