Yes, Obama should pardon Bradley Manning, because what he did wasn't that bad. Bradley Manning thought that he was doing the right thing. He needs to be kicked out of the military and told not to do it again. But punishing him criminally is not going to be a lasting solution.
Bradley Manning was convicted of leaking massive amounts of confidential information. With respect to the upholding of the United States government, he should be held responsible for his actions in his court of law, so as to not undermine the United States authority. Regardless of any government actions or offenses done against the American people, it is a direct act against the United States government to release confidential information.