|You know what I'm talkin' bout, Willis.|
For one thing, you have to admit that there exists a body of work that has been most influential in shaping the culture that you're talking about. You have to admit that a few select examples of a culture serve as fundamental instances of what that culture does, what it stands for, and what it means. For some, the very notion that a canon exits is problematic. They feel it constrains and hampers them, rather than simply defining them as part of the culture or not. That litmus test can be a very scary thing - it feels like a measuring stick that would shine a light on their own deficiencies. It would out them as imposters to the culture that they dislike, but very much want to control, to shape it more to their liking.
And so they claim such a thing simply doesn't exist.
This also results in the happy circumstance that the thing they don't really like - not really - can be remade to fit their own ideas. Rather than simply scuttle off and make their own thing, they co-opt an existing culture, and turn it to their own ends. Without a valid definition of the culture, without shining exemplars of the best that culture has to offer, they are free to redefine the culture. Which feeds back into the idea of "No Canon". They can then show those who built the culture that not only is there no yardstick, but even if there was, the early examples of the culture don't even fit the 'new and improved' culture.
Ah, but once a canon is shown to exist, then things get interesting. Then new works can enter the canon. The culture can change and evolve over time, and the additions to the canon will inevitable reflect the new spirit of the culture. Of course, that leaves in place the older canonical works, which allows them to continue exerting influence over the newcomers. And, more importantly, it takes a lot more time, effort, and skill to nudge a culture in a new direction. Why, one would have to compete with the old guard on a level playing field!
And so, if you want to change a culture, but are too stupid, too lazy, and too venal to participate in it, then your best bet is to deny the culture exists. Destroy its pillars, and then start stacking bits of rubble up in the ruins. With no majestic temple to be seen, you can point to your pitiful little stacks of broken rock and proclaim yourself the definitive example of the culture.
But those of us who remember the Cathedral you leveled will always know that you for the fraud you are, and we have ways of rebuilding the temple just as it was. And the more people see that temple and compare it to your sad little pile, the less influence you will have over the culture you so desperately wanted to control.
Sleep tight, frauds!