As far as I'm considered its about teaching respect as much as anything.
By going BC and putting kids in economy, its nothing like teaching them that they should respect their elders and adults get seats whilst kids sit on the floor. Its about we are too good for economy and we don't value you enough to be with you on a family holiday. You are not our equal and we do not see you as adult enough to be with us but still expect you to act like a grown up. Its teaching them to look down their nose at economy as its not good enough for mummy and daddy. Its teaching them that we frankly cant be arsed and we don't have any respect for anyone in economy and how our decision might affect others cos actually we are too bloody selfish to consider the possibilities.
There is nothing more irritating than being sat next to some stranger on a flight and having to deal with their kids cos the parents can't be bothered if if they are well behaved. Kids won't ask staff, especially if they are busy and if you see someone struggling, unless you are a total arse you tend to try and help them on a flight even if its annoying as hell. Because thats politeness and respectful (not to mention if someone if fidgeting next to you, it doesn't exactly help you get any rest)
In short Grade A Twattishness.