As you may know, Loughner has been ruled currently mentally incompetent and unfit to stand trial. But they're working on fixing that. However, I have read that the witnesses agree that he was completely insane at the time of the event and want him restored so that he "has no excuse." Well, if you will excuse me, I would like to give a different perspective
Suppose that you had lost control of your actions for a time. The madness had taken over. It's like another being controlling your body. During this time your body (over which you have no control) is used to commit attrocities that sicken you and that you would never do if you had the power to prevent them. Finally, medical professionals manage to cast out this other being (spirit, demon if you will.) But this is not because they want to restore you to a normal life in which you are a useful member of society again. They don't care about that. It's just that beings like that can't be punished according to our legal code and, since yours is the body that was used, they want to make you a scapegoat so that you can be punished for the rest of your life for things over which you had no control.
That, of course, is a nightmare scenario. I wouldn't wish it on anyone. But, unfoirtunately, there are a lot of people who would wish it on the defendant. Quite frankly, since they aren't going to restore him to a normal life like he would have had without the madness, there is really no point to restore him to a punishable state.