Those not subject to confiscation could still be used illegally

A comment at Commonsense Firearm Regulation (found via CH):

> those not subject to confiscation could still be used illegally
This doesn't really make sense as an objection. Most (I didn't check this, but I think it is true, including the most recent) mass shootings with AR-15s involve youngish people buying newish AR-15s. Taking out all the legal ones - most obviously including those in gun shops - would significantly raise the barrier to acquiring them. AFAIK, in general, school-type mass shootings don't involve criminals; so, ironically, you're not terribly worried about criminals possessing these weapons (for these purposes).