Because school shootings implicitly involve children, they can be a powerful emotional cudgel. Standing of the graves of children, politicians and demagogues can shout (and often have been videotaped) literally anything to get their agenda put on the cultural fast track. MAD (Mothers Against Drunk driving) did it with alcohol limits at the federal level. Using something cute and cuddly being annihilated is a powerful tool to stir emotion and shift conversation. Read Saul Alinsky's Rules for Radicals.