I have seen rudeness at Disney.
I remember a father who was FURIOUS that he couldn't ride Dumbo with both of his children at the same time (they simply would not fit). The CM tried to accomodate him - was even going to let him ride twice, but he elected to yank the holding area chain off of the wall, grab his kids, and storm off... neither kid got to ride, thanks to his actions.
I've seen parents yelling at kids for little things (not walking fast enough, dropping food, etc).
I've seen the parade pushers, the line cutters, the flash photo on dark ride takers, the yelling on Haunted Mansion riders, the runaway
scooter drivers, the ankle bashing strollers, etc.
You know what? I've also met a TON of nice people. I make it a point to be friendly while at Disney. When in a long line, or crammed on a bus, I talk to my neighbors (if they seem so inclined). Small chitchat - like asking where someone is from, how many times they've been, etc - can lead to fun conversations.
I've seen magical moments all over the place. I've seen parents tear up over moments involving their kids (and I have done the same). I've seen laughter, I've seen joy. I've seen people give away fastpasses, seen them let kids in front of them at parades, seen them give away snack credits (and done all of the above, myself). I've seen cast members make people's days.
The rude people make me angry, too. But people, don't let them ruin Disney for you. People are people, wherever you go. Sadly, there are no anti-rudeness fields that stop folks from coming on property.
Disney is what you make of it. If you expect perfection, you'll never be happy. If you expect to have a good time, and perhaps create your own magic (or at least let yourself be open to it), you will have an amazing time, rude people or no.