If you read the DSM-IV-TR you will quickly discover that everyone on the planet is suffering from some kind of diagnosable mental illness.
The minute they prohibit anyone who has a diagnosable mental illness from owning a firearm, you can bet that they will be able to prevent EVERYONE from owning one.
You just brought something else to mind. What about having access to weapons at work? If you're an armed security guard or a cop in marital counseling (that's outpatient therapy!), are you out of a job too? Or is home the only place you're not trusted with a gun? If you're a store owner who's on short term meds, can you no longer keep a weapon at work? And how in the heck would this apply to our active duty military and the mental health staff who treat them? The more I think about this the more I really don't like it!
Do you have a copy? I'm looking at mine now. Specifically at the disclaimers for its use in forensic settings (pages xxxii-xxxiii). I wonder if the feds will push the APA to strike these disclaimers from version V when it comes out in a few months.