He's have probably stood a much better chance of "getting off" or getting any aympathy if he had edited the documents and what was leaked before hand, the vast, vast majoirty of what was released was of no interest other then being to embarrass the US. had he simply released information about wrong doing, he may have carried enough sympathy to get somewhere and actually achieve something, but it appears as if he just compiled a load of stuff and then just dumped off all the info.
I don't think he can have expected to get away with it, if he did he would have just run to the nearest south american country with no extradition treaty with the US and gone to ground, I think he was genuinely misguided enough to believe he was a whistle blower, without actually taking the time to release only information that highlighted wrong doing rather than just some US diplomatic staff are muppets of the highest order.
He did it all wrong and thus deserves what he got, all he did was create large amounts of embarrassment to the US government and put lives at risk, and in all this any bit of good some of the information could have done was lost behind the utter drivel that was released.