Think of the children! You know, the ones who are too engrossed in their smartphones to look up anymore and are overprotected and helicoptered, not like the older generations who grew up dangerously without namby-pamby seat belts and political correctness and, by gosh, aren't lily-livered for it!
U.S. Supreme Court Justice Potter Stewart famously defined pornography in Jacobellis v. Ohio as such: "I know it when I see it." Some people don't consider Playboy proper pornography. Others think Cosmopolitan belongs in a protective sleeve and should be placed under a trenchcoat. Kirk Cameron saw porn in Growing Pains scripts in scenes where he and his girlfriend would lie next to each other fully clothed in bed, talking. We know it when we see it, and our eyes are all differently calibrated.
The effort to obscure Cosmo at the checkout counter is nothing new; Walmart's been doing it for about a decade, and other stores have since followed suit. They employ plastic black shields to block each side of the cover, where all of the copy blocks each month scream SEX SEX SEX (and the occasional "BE HAPPY AND IN CONTROL AT WORK").
To be fair, the checkout counter is a place full of idle children, and you don't want to turn it into a firestorm of awkwardness by exposing kids to concepts that they may be far too young to understand. Maybe stores should buck the psychology of the last-minute impulse purchase and place the magazine a little higher and/or a little farther away.
On the other hand, I was a kid once, and I don't recall ever taking even the slightest interest in Cosmo (I was too busy begging for the National Enquirer). But had there been blinders obscuring the cover, I might very well have asked my parents about it. And they probably would have pulled it out and said, "Because they don't want children reading about sex." And then Mom would probably have bought the issue, as she so often did, and left it all unlocked on the living-room table. And I would have been totally fine, because I was raised to understand that there was a big, mysterious, uncensored world out there, so maybe I should be mentally and emotionally equipped to handle it. Beats trying to block it all out.
When that doesn't happen, you really know it when you see it.