Prohibiting purchase of assault weapons would be a good start, but prohibiting possession would still be needed, and desirable. “A gun is a tool” says Wayne LaPierre. Hand grenades and rocket propelled grenades are also tools, but as much as I like my neighbors I don’t want them to have such tools in their homes.
The Second Amendment doesn’t authorize the possession of machine guns, tanks, flame throwers, nuclear bombs or other such tools. Neither does it authorize possession of assault weapons.
Our experience has shown that assault weapons are the tool of choice of mass murderers. Getting rid of them would not be the cure for our national madness, but it would be a welcome part of a cure. Speed limits on our highways do not cure automotive slaughter, but not even the National Rifle Association would use that as an argument for eliminating speed limits. I hope.