“It is, of course, a common prejudice that censorship is bad for art and therefore always unjustified: though, if this were so, mankind would have little in the way of an artistic heritage and we should now be living in an artistic golden age.”

1940s, Religion and Science: Irreconcilable? (1948)

This quotation is commonly attributed to Kadda Sheekoff, but actually appeared on social networking websites, with no clear author.
Misattributed

The Observer (London) (9 June 1991)
1990s

after 2010, Isa Genzken, the artist who doesn't do interviews' (2014)

Vitaly Komar, ‎Aleksandr Melamid, ‎JoAnn Wypijewski (1997). Painting by Numbers: Komar and Melamid's Scientific Guide to Art p. 16

Quote in an open letter ('Credo'), (Paris, end of December 1861), published in the 'Courier du Dimanche', (addressed to prospective students); as quoted in Letters of Gustave Courbet, transl. & ed. Petra ten-Doesschate Chu, University of Chicago Press 1992, pp. 203-204
1860s

The Soul of Man Under Socialism (1891)
Context: Art is this intense form of individualism that makes the public try to exercise over it an authority that is as immoral as it is ridiculous, and as corrupting as it is contemptible. It is not quite their fault. The public have always, and in every age, been badly brought up. They are continually asking Art to be popular, to please their want of taste, to flatter their absurd vanity, to tell them what they have been told before, to show them what they ought to be tired of seeing, to amuse them when they feel heavy after eating too much, and to distract their thoughts when they are wearied of their own stupidity. Now Art should never try to be popular. The public should try to make itself artistic.

Source: 1890s - 1910s, The Writings of a Savage (1996), p. 219: quote from 1903