Parents during the past 15 to 20 have sought to protect their darling children from even the slightest sting of the real world, which precludes shouting at them or hitting them or otherwise muzzling them when they start wailing in public. The parents just sit there trying to reassure the kid that everything's going to be OK, like all we have here is a failure to communicate, rather than a battle of wills. And of course everyone else is just supposed to sit there instead of walking over and pinching the little brat's ear.
I normally don't fly so often, but I've had several family get-togethers in the past couple weeks, so my memories are concentrated and vivid. Before I thought there might have been a problem with babies crying in the plane, but I'm convinced -- every single flight, there's at least one, usually two within earshot who periodically interrupt whatever everyone else was doing to howl away.
So to get a better handle on when this started, i.e. is it related to helicopter parenting, I searched the NYT for "crying baby plane." The earliest relevant article was from 2004, then there are regularly a handful of articles every year. What we really want to know about is babies crying in any public space where a certain level of peace is expected. There was an episode of Family Guy from 2001 that has a scene with a baby screaming its guts out at a fast-food restaurant, where everyone else is pretending to tune it out, but where the dog Brian finally snaps and gives the little squirt a good dose of his own medicine by howling back at him.
Any earlier examples? The phenomenon must have started a few years earlier than the first time it had become a standard situation for a sit-com.
By the way, this highlights another social disease that stems from helicopter parenting. When you keep your child insulated from all social contact that isn't strictly regulated by you (a la "play dates"), your kid is only going to grow up around genetically closely related people -- the other family members in his jail-house. Just based on Hamilton's Rule, they're going to put up with a lot of your kid's crap.
Thrusting him out into the real world where most of the people aren't close genetic relatives forces him to grow up and stop acting like such a selfish brat -- he'll figure out real quick that they don't give a shit about him, at least not like family does, so bawling his eyes out will not get him what he wants. In fact, it will have the opposite effect -- their patience will run out fast and they'll either beat him up or mercilessly brand him as a crybaby and a momma's boy.
Humans are a lot more altruistic than other primates, and one reason known about for a long time is that we spend lots of time around others who are far less genetically related to us than the nuclear-ish family members that most primates hang out with. So they can be incredibly selfish and not get called out on it so harshly. Just let a human being try that, though, and watch how quickly he's set upon or driven out.
How odd that the same parents who would have a stroke unless their kids eat the organic brand of Pop-Tarts, have robbed them of the most basic element of human nature -- sociability with genetic strangers. Only slightly more disturbing is the kids' decision to go right along with that perversion of nature, rather than disobey their parents when the grown-up world has grown out of touch.