It depends on the player, if your glued to a lane hard scoping all game then yes it's cowardly. But most people I know play no less aggressive than a shotgunner, pushing forward and using snipers to get a quick kill if confronted by another sniper or a small group to thin their numbers before getting into primary weapon range. Shotgunners more often than anyone will overestimate their ability and make dumb plays by rushing into a crowd. Sometimes you may win but it still isn't a smart play. Tl;dr sidearms ftw