There will always be people in gatherings as large as Disney that will be rude, mean, complain about anything/everything, obnoxious, whiney, contentious, and anything in between, and let their kids be brats - unfortunately, that's what some humans will stoop to.

They are 'not' happy people. We just move on.
Fortunately, there are 'more' good people.
We've learned to enjoy ourselves and try to ignore what we can do nothing about. If we can help, we will. Otherwise it can ruin our happy feelings, and know that Disney is what we make of it for ourselves. Just got back from a 10 night happy, relaxing trip.