I am a parent. I have a three year old who flies at least once a month (and has since she was three weeks old) and a nine year old stepdaughter who flies a few times a year. Both of the girls are well behaved most of the time because they have rules and expectations. I realize you can't do that with infants, but you start talking about it and ensuring you are well prepared.
I am sick and tired and kids running around and misbehaving at restaurants, play areas, doctor's offices, and yes, airplanes. It reinforces even MORE why I want to have rules and expectations for my girls. I do not understand why parents find it acceptable that their kids are kicking the seats in front of them and I simply do not understand why ANYONE at ANY TIME would change a diaper in seat. In the many flights my daughter had her first year, there was never an occasion that would have necessitated this and I can't think of one that would have.
Where have manners gone? People, before you have kids, take a good look at yourself. Are you considerate of others? Do you say please and thank you? Do you jerk the seat up of someone in front of you? Say rude things to other people/passengers? Then guess what? Your kids will pick up on that and be the kind of brats we're all upset about in this thread. They mimic everything you do and pick up on your behaviors.
I am far from a perfect person or parent. I know that my daughter has to fly at least every month (we visit her sister in California) and I knew she was not going to be the type of flyer I cringed around so I started doing things early to ensure she wouldn't be. Still, she's not perfect and has had her moments on flights - thankfully these have been few and far between.
I don't think the answer is to ban children to coach and I'm sure the airlines won't think that's the answer. The answer is for parents to take responsibility and to teach their children how to act appropriately in public situations.