That's exactly the sort of information that needs to see the light of day. It should not be hushed up and hidden behind a purely military investigation. The American public have a right to information about those kinds of issues, just like we have a right (and a responsibility to know) about what happened in the hidden prisons at Gitmo and in Abu Ghraib.
On another level, Private Benning clearly violated the law and his sworn oath, and he didn't stop with releasing the single incident, but went much, much further to release reams of information that were not necessarily evidence of a government coverup, and in fact, of which he had zero knowledge or understanding.
Private Benning will have his day in court. It's up to the jury/judge (and, frankly, history) to decide whether his actions were traitorous or heroic.
Let me ask those who are so quick to condemn him, though. Do you think Daniel Ellsberg was a traitor or a hero?
I think history has determined that he's a hero. So, what are the crucial differences between Ellsberg and Private Benning?