Ban Weapon Propellants (Score 1)

This is a preventative suggestion, and with a nod to Chris Rock's 'control the bullets' bit.

Either ban or heavily tax the propellants used in any way to propel some object an offensive or defensive manner (eg: bullets and missiles). People can still kill each other with a variety of state-of-the-art gizmos, NASA can still have its space program, and we'll have a cleaner atmosphere.