He should have contacted an attorney or the Justice Dept instead of some random internet trolls. He took an oath and he broke it. If it happenned during WW2 he would have been on the business end of a rope and long dropped over a bridge.
Since you're reminiscing about the good ole days of WWII, let me remind you that back then you'd have been cannon fodder, if you hadn't already been hung from that same bridge for being a sexual deviant.
Manning's oath, ultimately, was to defend the Constitution. He saw horrific abuse by the US Governmenf and he decided to expose it. He broke a confidentiality agreement that he signed with the government in order to do so.
Petraeus broke the same agreement. He shared far more valuable and highly classified data and for much less admirable reasons - basically to impress a chick and get his dick wet. And you're fine with him receiving no punishment at all. I can't help but feel you're being a bit of a hypocrite.
As for going through appropriate channels, we saw how well that worked for people like Snowden, Binney and Klein.