Your sense of humor or what you like in a horror movie does not make you smart or dumb, it's just what you like.

That's not even close to being true. A "sense" of humour or taste in some cultural or aesthetic thing is not born from some ether of individualism. Tastes and "senses" are built culturally, economically, and ideologically. So this means that there's neither an objective quality to aesthetic nor a purely relativist appreciation of it. It comes from somewhere, and that "somewhere" is related to education and class (among other things)--like it or not.

This isn't the same thing as saying that only dumb people will like IT and only smart people will like Kubrick. When Mike and Jay talk about the consumption of certain movies, and their popularity, they speak as people who are experts (also like it or not) - filmmakers, producers, editors, writers, critics, and, at least for Jay, historians. The simple fact is that they know more than most other people about movies, and that trumps the "I like it because I like it" argument. They can't meaningfully tell you NOT to like it, they can't necessarily call you stupid for liking it, the things they like don't necessarily have any relationship to their expertise, but it does mean they can spot cookie cutter repetitive shit built by money-making enterprises just fine. If you like something while realizing it is of that sort, that still isn't a completely relativist thing.

What you like comes from somewhere. At the very least Mike and Jay know what they're talking about (and what they like) and why. That's the difference.