These days, “Fifty Shades of Grey” and its two sequels are everywhere, in print: on the racks in airport bookstores and on library shelves. This highlights a fact that is understood by marketers and any number of Hollywood executives, but often unacknowledged by politicians: Human beings, even Americans, like sex. And this bears repeating during the hard-to-kill debate over the women’s preventive services mandate in “Obamacare,” which requires that, starting in August, all health plans have to offer contraception free of charge.