Last night, July 23rd, 2009, I finally saw Die Hard.
It's an excellent movie, all told, even with me knowing how it ends, even with me having seen so many movies that tried to ape it. I knew the important quotes already, of course; I had to, because otherwise I couldn't survive.
See, in the circles I run in (probably most decent circles), Die Hard is one of Those Movies, similar to Those Books. I'm sure you've got some of Those in your circle of friends, too*; those works that everyone has to have seen, or they can't be in the club. Those works which, when a person confesses to ignorance of them, trigger gawping and gasping and stares of disbelief. Critical circles have those, too: books like Ulysses, or movies like Citizen Kane. Only in critical circles it isn't usually staring, so much as it is dismissal of any opinion not partially empowered by those works.
This attitude is part of the problem.
I think it's fair to say I'm a pretty smart guy. Well-informed, most of the time, pretty well-read and educated. But I am paralyzed at the thought of admitting I don't know some particular piece of film or literature, due to the possibility that the reaction will be "Oh My God how could you not know that piece you infidel?" It has happened so many times and with such vehemence that I am reluctant to admit pieces I don't even expect the people I'm talking to would care about—particularly since I got my Master's degree and am now, in theory, the Well-Read Guy in my social group.
Now imagine people who are less secure in their intelligence. In their acculturation. Their education. Their taste. Think about the impact this kind of reaction has on them. Why even bother trying to be well-read (well-viewed?) if you're going to get mocked for seeking out the quality works?
I'll freely admit I'm a sensitive guy, but this doesn't just have to be about feeling insulted. I know plenty of people who haven't seen what I consider great movies, purely because too many people have told them they "have" to see it. That kind of hype never pans out well; there's a reason TVTropes has a whole bundle of entries about the reactions triggered by hype.
This is one of the places the Internet has not improved things in the slightest. With communication globalizing, people can pick on your taste and your apparent lack of culture from across the globe, and your chances of encountering someone who thinks the works you do not know are seminal approaches one with alacrity.
I am fortunate enough to have made friends who do not do this; who react by saying that a piece is great and offering to lend it to me, rather than even mock outrage. I still have some friends who do it, but they also tend to like different things than I do. And also I'm inured to it.
What I'm saying here is that I think canonization of media is dangerous. While I won't pretend there aren't movies and books that are just plain better, I also won't pretend that there isn't a huge amount of subjectivity involved in determining what does and doesn't suck real, real bad. And I agree that there are some works that people who want to study a genre or technique should read for good examples of them. But I don't agree that those works are universal or that not having read them voids one's opinion on a topic; that's a tactic for debate of facts, not taste. And reacting as though there is something wrong with the lack of exposure is not the best way to remedy it.
So the next time someone says they haven't seen a movie, pause. Your shock could be the reason they never check it out again. And please, please, don't use the word "canon".
*I'm going to guess, given that you're here, that your movies probably include Mirrormask and/or Pan's Labyrinth, and you probably list The Sandman among the books. I can dream.