OK. Let me try it from another angle. Suppose a cast member with a megaphone announced to everyone in line for F! that today they were going to try something different, as long as everyone agreed. She offered that "if everyone in line was in agreement, we will allow one member from each party to remain in line and the rest of each group could go enjoy the park. 20 minutes before the show, everyone would be expected to be back in line right where they were before. By a show of hands, is there anyone here who thinks that this is a bad idea?" If offered this opportunity, there is no logic to refusing the offer and no benefit to be derived from turning this down. Everyone, unanimously, would take the CM up on her offer. Why? Because all of these people, collectively, decided that if everyone was to benefit equally, then it is not "rude" to enjoy this benefit. "Rude" is merely a state of mind that can be overcome if everyone participates equally and no one is getting hurt.
In the same vein, if you were next to last in line and the people behind you who were dead last tapped you on the shoulder and said: "I wouldn't mind if your family got out of line and enjoyed the park as long as one person stayed to save a place in line." If that offer were made, it would not be "rude" to take the person up on the offer because you have his permission. To share the pixie dust, you tap on the shoulder of the person in front of you and make the same offer. That person takes you up on it and taps the person in front of them, and so on and so on until this reaches the very front of the line. Every person has given every other person in front of them permission to engage in the behavior. So you see, rudeness is simply a function of permission. And if everyone in the world gave everyone else in the world permission to do something, then doing that thing ceases to be rude. If every Disney visitor agreed in advance with every other Disney visitor that having one person in line for F! is sufficient, then it wouldn't be rude to do so. So while I am in no way advocating that people act rudely, what I am suggesting here is that if everyone agreed to "virtually" tap each other on the shoulder and say: "I wouldn't mind if you took your family out of line to enjoy the park as long as you extend the same courtesy to me", then we would all improve our day at the park.
(Sorry. I really should have made this point in my first post as I think it is the most simple and noncontroversial way of looking at this. But I didn't think of phrasing it this way until now.)