In an earlier post I seized on the sentence: "The strongest objection to the more trivial popular entertainments is not that they prevent their readers from becoming highbrow, but that they make it harder for people with an intellectual bent to become wise in their own way."
This sums up most of my objections to masscult. The more of it we have, the more places in our culture that aren't masscult are crowded out and pushed off the market, and the net effect is a flattening-out of culture. Or, at the very least, a siloing, where great things are happening next door but you never end up hearing about them because the walls are so thick.
It's not just that the money that could be spent on one big dumb blockbuster could also be spent on a dozen other, better, more modest films (although that's part of it), it's that the presence of such things in our culture becomes disproportionate. It becomes harder to find out about anything outside the mainstream masscult reality tunnel, because fewer people have an incentive to talk about it. The few news outlets that continue to carry a movie page mostly report about gossip or blockbusters that everyone already knows about anyway; few of them bother to talk about what the movies can be at their best anymore.
The "paradox of choice", as Barry Schwartz put it, has been making the very plurality of our media into its own worst enemy. George Lucas once opined that the multiplex was going to be a good thing for cinema, because it would mean that smaller and more personal fare could play side-by-side with the big tentpole productions. Nothing of the kind happened, of course: we now just have theaters where the latest blockbusters are shown in three different theaters with a new showing every twenty minutes, in your handy choice of 2D, Dolby 3D, and 3D IMAX HFR. The end result of such plurality isn't diversity of independent taste, but again a siloing effect, where people find the few things that cater to their existing tastes and then forget that anything else exists.
People discover things when they can enter and inhabit a space where there are few walls, and they discover them there in a way that doesn't have an exact analogue elsewhere. If I go hock my books at a con, I'm able to sell most of what I bring with me, because the people there have entered that place assenting to be marketed to, so to speak. Ditto a bookstore: we put things in a bookstore because people come there to be marketed to in a controlled way. Browsing on Amazon, much as I love doing that too, is still a lousy substitute for all this.