The documents regarding that incident were pulled from an Inspector General's folder regarding an open investigation. That hadn't shown themselves to be anything. They were actively looking in to the incident. If anything Manning tainted the investigation and may have even prevented justice from being served.

There is a difference between releasing data that is strictly related to the public interest and taking massive amounts of data, including information about very sensitive operations and diplomatic discussions and releasing them without regards to the damage they may cause. It's reckless.