We can't. Any means of effectively protecting schoolchildren from school shootings would by definition be an abridgement of the public's right to keep and bear

We can't. Any means of effectively protecting schoolchildren from school shootings would by definition be an abridgement of the public's right to keep and bear arms, and thus unconstitutional. For some reason the First Amendment is a lot more negotiable for the American public than the second, so banning books will probably never be as politically intractable as banning guns in the US.