One doesn’t often see these three things discussed at the same time. It’s commonplace to hear people talk about the arts as if the operation of markets were completely irrelevant. 
Similarly, many philosophers think that the arts are a second-rate way to communicate philosophical ideas, and that markets cannot be trusted to operate on their own. Artists may well be skeptical of philosophy’s propensity to over-analyze. But there’s room for cooperation and mutual understanding.

Plato is often thought of as harbouring deep antipathy towards the arts. The cliché is that Plato wanted to banish all the artists from his ideal city. This is a misunderstanding. Where Plato comes near to saying anything like this, it’s a fictional dialogue in which the main character is weaving an allegorical fable. So it’s literally impossible that he meant to suggest that the arts were useless in motivating philosophical discussion.

On closer inspection, Plato’s point seems to be that because the arts speak more directly to the emotions, we must be wary of manipulation. While discursive reasoning must be accepted or rejected on standards of logic, an attempt at persuasion via the arts may succeed where reason would not—think of the propaganda films of the Nazi or Soviet periods, or D.W. Griffith’s film Birth of a Nation.

So the arts can be used to communicate an idea, and even to persuade, but this can be done for good ideas or bad ideas. The only way to distinguish the two is by applying our rational faculties in the assessment of the ideas. This is a better way to understand Plato’s concern: our tendency is consume the arts passively, without engaging our critical faculties, and this can result in our being manipulated. But if we approach the arts with our critical faculties hovering in the background, we can guard against that manipulation. This is one reason Plato uses a “guardian” metaphor for our rational faculties. That need not imply censorship from on high, since the mind is individual. So philosophy and the arts can work nicely together—as Plato himself realized, artistic representations can often facilitate, rather than impede, our understanding of things.

Aristotle, often presented as diametrically opposed to Plato, would agree on this point, and indeed has a theory about how the arts can be morally edifying. (They can also be morally corrupting, but Aristotle seems a little more optimistic about people’s ability to apply filters to their perception of the arts.)

What about the arts and the market?

Artists express themselves through the creative process, often to satisfy their own sense of purpose, but clearly there is a market for the arts:  museums are often crowded, and thousands of artworks are produced every year for wealthy patrons as well as for general consumers. Wealthy patrons have always been “sponsors” of the arts, but so too is “the market” a sponsor of the arts, in the sense that the majority of non-wealthy people also enjoy consuming art. Novels, music, film, television, painting, decorative arts—these are not the sole province of the wealthy few. That art is all around us tells us that art is a market phenomenon.

That is not to say that what is popular is identical with what is good, or that what is unpopular is not good. But it’s true that there is a demand for the arts, and a multitude of would-be suppliers.

An open market for the arts is the best way to allow artists and their patrons to connect—for the “supply” to meet the “demand.” Censorship interferes with this process, to the detriment of all. Bad art can emerge, as can bad ideas, but the best response to this is engagement of the critical faculties. Just as that is the only way to distinguish good ideas from bad ones, it’s the only way to find the art you value.