That thought process means no individual should ever sell a gun, car or even a pointy stick.
Claiming a some ambulance chaser could sue, doesn’t mean the suit would have any merit.
Lots and lots of guns have been used in crimes by mentally defective people. If such a claim had any standing, it would be a common lawsuit. It isn’t.
The Dems are trying to make it ‘common’:
http://www.propertycasualty360.com/2013/04/12/insurance-industry-closely-watches-proposed-firear