While I do believe that some truths are better off buried, I think government's privilege to classify documents is a tremendous power, and one it is bound to misuse. For this reason I applaud the work Wikileaks is doing. I don't think Wikileaks, and other journalistic organisation for that matter, should use other criteria than veracity when deciding whether to publish. With any classified information you could always come up with scenarios where lives might be endangered or other bad situations might occur if it should be revealed. And so, slowly, gradually, you would become a lapdog of those you were meant to guard against.
I think it is the government's responsibility to keep documents it doesn't want published from falling in wrong hands, or preferably avoid doing things that need to be classified in the first place. As for atrocities, the moral responsibility falls upon those who commit them.