Well, I'm a bit late to this discussion, and George beat me to the point that Assange cannot be guilty of treason, so I'll just comment on this one statement:
"If they were diplomats that authored the cables, and they leaked them because they felt it was morally right (or whatever reason you can think of), that is a different story because freedom of speech can apply there since they would have been the authors."
Uh, no. If you work for the government (e.g., as a diplomat), then you give up some freedom of speech--particularly when it comes to classified info. If you work for the gov't and want to say how wrong the gov't is with some policy, you may resign and then speak your mind.
I'd also note, just for the fun of it, that leaking of classified info goes on all the time and it's generally not done by PFC Manning's of the world but by senior people. (They, after all, have access to the secret stuff.) It is how the news world operates.
As the Sec Def put it, "The fact is governments deal with the United States because it's in their interest, not because they like us, not because they trust us and not because they think we can keep secrets." Other "governments deal with us because they fear us, some because they respect us, most because they need us," Gates said.
Cheers,
Steve