Earlier quoted context omitted.
Classifying material should not be a way for the Government to hide corruption and wrongdoing. Whistle blowing is the only way that prevents that. Chelsea Manning acted on her conscience, which is the best we can expect anyone to do. The governments punishment was to prevent that happening again.
Manning dumped a whole slew of stuff without any checking or vetting or anything else. Some of the stuff I saw in relationship to Italy, for instance, was just diplomatic personnel airing "what they really thought" about Silvio Berlusconi. These comments are the kind of thing that didn't do anyone any good to have dumped in public.
The thing to keep in mind, though, is that Manning didn't simply dump these to "the public"; she gave them to Assange and his people, who (after some falling out with each other, and a lapse in some basic security practices) managed to leak the passphrase to one of their private keys.
Which isn't to say she's not responsible for the consequences of her actions; in any case, she's already very much paid the price for the decision she made. But still, it was not her intent that the cables be simply "dumped in public".