In a 6-3 decision along partisan lines, right-wing justices on the U.S. Supreme Court ruled a bump stock, an accessory used in America’s most-deadly mass shooting, that effectively turns an AR-15 into a machine gun, cannot be regulated under current law. Justice Clarence Thomas authored the majority opinion. The device is so dramatically lethal pro-gun President Donald Trump banned it in 2018. “The Supreme Court just effectively legalized machine guns,” is the headline of Ian Millhiser’s report at Vox. He says Friday’s ruling “effectively legalizes civilian ownership of automatic weapons.” “Bu…