You're absolutely right. Contrary to what parent claims, the US and our allies do a lot of good around the world that is made possible by having strong international diplomacy with other countries.
If there are 'criminal' political back-dealings, then don't the people perpetrating them, bear some responsibility? Otherwise we end up in the 'too big to fail' position where anything bad these people do will always be covered up, and they basically get a blank cheque to do what they please. (by 'people,' I mean the specific politicians/diplomats/etc involved).
After reading this thread I've come to the conclusion that it's ethical to leak secret government documents (from a democratic country) if and only if the document provides evidence of someone in the government behaving illegally.
Random dumps of four hundred thousand random government documents, however obtained, don't cut it.