I don't see where's the problem, IMHO.
Not that the question would have a damn thing to do with medical science, but the doctors aren't just asking.
It has to do with medical malpractice. If someone is a threat to themselves or others, docs could be sued if someone is shot. I would have preferred that Gerald Loughner was committed in Arizona before his murderous rampage.
All the viable mental threats I have encountered over my years as a sheriffs deputy etc ....have been been very quiet people.
Sort of the barking dog never bites theory I use.