Some of it is disney's fault. All the cut backs, increase in the price of everything, and all done over and over these past few years. Human nature puts all this together and the reality hits of lines, frustration all around, waiting from the morning til 2pm for a preordered hot dog, just a number of "things" that add to the frustration. Plus the fact everyone is paying ALot of money just to be there. I've seen poor behavior increase as the crowd levels increase, the lines increase, the prices increase.
Of course, they are not responsible for violent guests, but put all the frustrations together and some people can't handle it. I've also seen the entitlement card played too. "I;ve paid all this money and I will cut this line or I will push my way past everyone to beat them to 7DMT". Maybe they didn't see it coming? But it seems to be happening more frequently at the "magical place on earth".