According to a report by the National Academy of Sciences published May 2, the incidents of so called “air rage.” Air Rage is unreasonably aggressive behavior against cabin attendants and fellow passengers. It is closely related to the increase in First Class seating.
It appears that air rage is actually triggered by economy class passengers being confronted by the fact that a privileged group is having better food, more comfortable seating, and generally better treatment than they are getting – this causes the normal tensions caused by the cattle car crowding of economy class seating to boil over when there is any additional problem.
According to the report published in the Proceedings of the National Academy of Sciences, “researchers found that flights with a first-class section were nearly four times more likely to have air rage incidents in their economy class, and that these incidents of ‘belligerent behavior’ or ’emotional outbursts’ became nearly 12 times more likely among first-class passengers and more than twice as likely among economy-class passengers if people were made to board from the front of the plane and walk through the first-class section together.”
“Stark differences in class,” are thought to be the base cause of various recent incidents and not just in airplanes.

But as common as incidents seem when you see daily news reports on TV, the number of air rage incidents has actually declined to only about 112 REPORTED incidents in 2014, down from more than 300 incidents reported in both 2001 and 2004 as pointed out by The Washington Post.
Air rage is obviously an irrational act since it is usually a complaint about something over which the aircraft crew has absolutely no real control. It can be punished by a fine of up to $25,000, even a jail term in some cases. Until fairly recently, most incidents weren’t really punished, which could be another contributing factor in the past increase and the current decrease now that a zero tolerance policy is in place on many airlines as well as the FAA.
It is, of course in the interest of the airlines to make first class much more attractive than economy and to make economy class seating a generally miserable experience in order to encourage more people to pay a much higher fee to fly in relative comfort.