The Rosenbergs were caught by legal counterespionage actions (which included SIGINT!) properly tried and convicted. However the difference is Rosenbergs were naturalized citizens, assigned to the Manhattan Project and therefore under signed obligation with full knowledge of the consequences of violating that obligation to protect US secrets. The only one in the currently WikiLeaks affair who at least as I see it has an obligation to protect those secrets is Manning. He failed to do so, apparently over some failed gay lover affair! Again past relaxation of security standards are coming back to haunt us and the Zero administration wants to relax them more!
Right now all we now about Assange is he is an Australian nihilistic anarchist. He might be an agent of a foreign power but even then there is NO evidence he is anything more then a receptacle of secrets not a tasker of acts of espionage. Basically he put Wikileaks out there on the web and invited malcontents and sociopaths from around the world to give it content. It would be a stretch to call that “espionage tasking”. Right now I can't see how he has violated our laws, Manning violated the law and his soldierly duty. He needs to pay dearly for his actions.
Assange right now has to answer for his "social" actions in a Swedish court which apparently have to do with underage rape. He isn't a Muzzie so maybe Swedish justice won't be intimidated, and I hope Swedish prisons are very cold!
>>except we have never done extralegal killing for acts of espionage<<
It is a new world — no time like the present to tell the world we will NOT allow our secrets to be published and that we WILL take action.
And such action is not “extralegal.” It is 100% within international law guidelines.