I do not believe that you believe that Manning read all or even most of the documents in the dump. I think you believe like I do that there were a large number of documents in that dump he hadn't read, and could not have judged the safety of leaking.
Even if I grant you that for the sake of argument, what you are saying amounts to "he guessed correctly, but only accidentally, so we should still charge him as though he guessed incorrectly."