We don't need to make leaking all things all the time legal, but we need our legal system and our courts to have the option to decide whether or not something is in the people's best interest to have released and then pardon those leakers on a case by case basis, punishing those who aren't. It's a case of balance.
The Supreme Court may be the final arbiter (within the system of government, at least) when there is a controversy over what is constitutional, but it does not mean that they are the only entity that has the power or obligation to interpret and act on the Constitution even when other laws purport to mandate something contrary to it.
> but the Espionage Act exists for a reason.
The Espionage Act may exist for a legitimate reason, but the manner in which it purports to serve that reason has been the subject of serious and sustained criticism from pretty shortly after it was adopted nearly a century ago.
It might be a good idea to rethink it from first principles, rather than accepting a framework laid out in the early-20th Century Red Scare and then tightened under McCarthyism.
You can't really say "the law", since a large portion of what the NSA is doing is legal under the PATRIOT Act and various intelligence bills and processes. And you can't really say "the Constitution" either, since only the Supreme Court truly possesses that power.
I do think Snowden should be pardoned, and I think his intentions were pure and he mostly acted properly (though I do have a few issues with some aspects of how he handled it), but the Espionage Act exists for a reason.