I've asked several times IF it's really the widespread problem that people make it out to be. If it is, then things have definitely changed dramatically in the two years since I've been there. I've also stated (more than once in this thread actually) that I have not personally experienced line-cutting, or that if it was going on, that I haven't taken note of it.
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Now having said that, am I inclined to believe that people are exaggerating the problem? Probably yes.
I think the truth surely lies somewhere in the middle. I think it's a virtual guarantee that at least some people are exaggerating. I also think that your very attitude (about which I've already expressed admiration, I'm not criticizing you for it) virtually guarantees that there have been such incidents in your immediate vicinity without you being aware of them.
I'll also offer the observation that when I have seen people cutting in line, they are almost always doing it by crawling over or under the fences separating lanes in a switchback - meaning that in most cases, all but a few of the people in line are completely unaware that it even happened. I almost never see people passing through the line in such a way that they have to actually cut in front of each and every person ahead of them to reach their party.
My own experience is that it does happen, it happens fairly frequently (I probably see it on every perhaps third or fourth visit - and my visits are usually a few hours and involve just one or two attractions, if any). I don't feel like I'm being hypersensitive, or watching for it. When I do notice it, it's usually because the culprit is doing something else to draw my attention, like being generally loud or boisterous, or running up to the point where they're going to jump into line, or what have you. If you make the assumption that most people are sneaky about it, then even my own observations probably under-represent the frequency with which it actually occurs. I don't have any sense that it has gotten more or less prevalent in the almost 10 years I've been an AP holder.
Regarding scale, it's true that the impact, even at the high end of a full minute per incident, is small most of the time. The only counterexample I can think of would be a show like Philharmagic or Tough To Be A Bug, where if they are playing to full theaters, each group of line jumpers causes the last few people who should get into the next show to have to wait for the following show, costing them maybe 20 minutes but having no impact at all on anyone else. On the aggregate, that's no different than taking a few seconds each from a few hundred people on a continuously moving line - unless you're the one losing 20 minutes. Bottom line, though, is you're right that it's almost always not a big deal.
But perhaps that's not always the point. I've already said more than once that I could care less about the impact to me personally of someone cutting the line, even if there is an impact. If I only get to ride Buzz Lightyear twice instead of thrice today, or I miss Wishes, no biggie because I'll just come back and do it next weekend. But that doesn't prevent me from caring when I see it being done to others. And some times, may God forgive me, it would just be nice to see someone who is doing something wrong suffer some consequences for it.