The issue here, sadly, is that as pax we've already undergone a myriad of unpleasant experiences just to get on the aircraft.
Then most of us will endure rather than enjoy a flight, especially long-haul in steerage, so the veneer of civilised behaviour we all wear in public - well, some of us, anyway - is already worn pretty thin by the time we're at cruise. It doesn't take much by that point for more primitive instincts to break through.
That's not to condone bad behaviour but, I believe, to explain it.