I don't know if the efficacy of the weapon for hunting is really that relevant - if there was (hypothetically) strong evidence showing that banning AR-15s could actually prevent school shootings, then obviously you would want to do that. The efficacy of something for a recreational sport does not supersede the right for kids not to die in school.
Again, not saying a ban would work. I think there should be more legislative 'trial runs' to collect data on what regulations actually work.