We tend to do long flights. There have never been any drunken adults on board, but often some children. But they have been fine. I suspect parents of badly behaved DCs don't attempt 16 hour flights with them. Exception was one toddler who constantly kicked my friend was sitting next to him, and whose mother complained loudly when she told him to stop. Also on long flights you have entertainment systems, so DCs are usually just watching kids films.
I do think parents should not be able to book First Class and put their young DCs in economy. I ended up sitting next to young DCs whose parents came down every so often to check on them from First Class. They were well behaved, but I still ended up partly looking after them by helping them to sort out problems with entertainment system, to adjust air vent flow, open a drink for them, etc etc.