If you want to use a car for lawful purposes you would buy it. However if you want to use it for unlawful purposes you would be much more likely to steal it. For the most part injuries caused by driving are by lawful drivers that want to obey the law. Traffic safety laws help those people drive safer. Gun violence is caused by lawless people. Those people are already violating the law to do what they want, new laws won't change their behavior.
I didn't specifically say allowing firearms on airplanes would make them safer. I said that you would eliminate some problems while increasing other problems. I said you would stop all hijacking but there would be a few more random shootings. I really don't know what the net result would be.
How do YOU propose to take guns out of the hands of criminals?