Parents need to understand that it’s not polite to allow their kid to scream in public. I get that it happens and in rare circumstances it’s unavoidable. If a kid is having a hard time in a supermarket the parent can remove the kid from the store. The parent can remove a kid from sacrament meeting.
The parent can not remove a kid from a plane so other options must be available for the parent. My wife allows each kid a backpack of fun things for a kid to have on the plane. Coloring books, snacks, headphones to watch movies on the iPad, etc. my wife also packs gum for when a kid’s ear won’t pop. Parents need to be willing to give their kid what they need so as not to cause problems for other passengers on a plane.
I read an article about a parent who even made little gift bags for other passengers. This is dumb and not effective. It was a nice gesture but unnecessary. People just want a peaceful flight.
I can understand when a kid has a momentary tantrum, but if a parent ignores it and it continues with it being a bother to others then that is not ok.