KAROL MARKOWICZ: The decline of sex is the end of civilization. “This should be a golden age for sex — if not the swinging from the chandelier kind, then at least the regular, reliable fun type. The economy is booming, and America, and the world, are safer than ever. Young people can find willing mates just by swiping on their phones. It’s a cushy, luxurious time. So why aren’t we naked and rolling around in bed to celebrate? Speculation is rampant.”