It is. Our constitution is pretty clear that what Mr Assange is doing counts as Freedom of Speech. The crime is commited by the people who leak the information to him.
Which is also true under US law. See the publishing of the Pentagon Papers or Bob Novak exposing Valerie Plame. Neither the NY Times or Novak broke any laws.
That's a fundamental misunderstanding of both the Pentagon Papers case and current law. The Pentagon Papers case was about whether the government could stop the New York Times from publishing classified information, not the criminality of the actual release. And the government sometimes has good reasons not to go after lawbreakers who release classified information, including not compromising additional classified information during the trial.
LOL, "espionage", "treason", "foreign spy". Good luck getting him extradited to a country that still has a federal death penalty for such offenses, guys.
Who said anything about extradition? There are plenty of ways governments deal with foreign spies, many times not by hauling them into court.