After the Newtown school shooting, commentators on the Left expressed outrage that gun-rights groups were exploiting the attack to build membership in the wake of all the liberal demands for a federal crackdown on gun owners. Nine months later, they’re curiously silent as Rupert Murdoch’s cable network FX milks a fictional Catholic-school shooting for commercial gain. The Sept. 10 premiere of the violent motorcycle gang drama “Sons of Anarchy” featured the school shooting, as well as two rapes and a man drowning in a bathtub of urine.