The problem is with the parents; not the child. Just as it is unacceptable for a child to scream in a movie theater, a parent needs to sternly tell their child that unacceptable behavior is not tolerated.
My boy is only 11 months old and at this young age travels well. However, I know that he will not be as easy as he gets older. My plan for future travel includes taking along many toys and books and giving them out one at a time as he gets bored with each thing. Also, taking along a few favorite snacks, taking walks down the aisle if it is a twin aisle plane and taking night flights or segments that are not too long.
In other words, any of you would be glad to fly with me and my son.