I doubt the Chinese government thinks that that agent is a good guy, hence it's not objectively true. The problem with what you're proposing is that it requires a very high level of editorial censorship. Who should perform that censorship? I've spoken with Americans relatively recently who still believe that the Iraq war was totally justified, or perhaps just didn't need justifying in the first place. If they are responsible for that censorship very different things will be censored than if I do it.

Saying that only items indicating crimes should be leaked is a very low bar. How many people using that standard would choose to release the cables about the German citizen who was abducted and possibly tortured? In the other thread about these leaks here on HN that is dismissed as a "mistake", something that's impossible for me to fathom. It's basically saying that collateral damage is OK if it furthers the US interest.

I'm not arguing the specific case of the politburo agent here since I haven't read that part yet, but your claims that it's easy to decide what's right and wrong are naive at best.

Edit: Downvoters, feel free to leave comments disagreeing with me.