In what could be a watershed moment, gun-control advocacy in the U.S. has won support from large corporations after the February 14 massacre at  Marjory Stoneman Douglas High School in Parkland, Fla., that claimed the lives of 17 students and educators. The National Rifle Association (NRA), the flag-bearer of gun rights, found itself in the sights of Delta Airlines, United Airlines, Hertz Rental Cars and MetLife, among a growing list of other businesses. Also, retailers like Walmart , Dick’s Sporting Goods and Kroger decided to stop selling guns and ammunition to those under the age of 21; the current legal age threshold is 18 years. Others like Amazon, UPS and FedEx have resisted calls to break ties with the NRA. All those moves have come after survivors of the Parkland shootings launched the #NeverAgain campaign to combat gun violence with stiffer legislative controls.…