“The only excuse for making a useless thing is that one admires it intensely. All art is quite useless.”

The Picture of Dorian Gray
Variant: All art is immoral.

Source: Down and out in Paris and London (1933), Ch. 31
Context: Beggars do not work, it is said; but then, what is work? A navvy works by swinging a pick. An accountant works by adding up figures. A beggar works by standing out of doors in all weathers and getting varicose veins, bronchitis etc. It is a trade like any other; quite useless, of course — but, then, many reputable trades are quite useless. And as a social type a beggar compares well with scores of others. He is honest compared with the sellers of most patent medicines, high-minded compared with a Sunday newspaper proprietor, amiable compared with a hire-purchase tout-in short, a parasite, but a fairly harmless parasite. He seldom extracts more than a bare living from the community, and, what should justify him according to our ethical ideas, he pays for it over and over in suffering.

Referring to his rival Raymond Poincaré, as quoted in Paris 1919 : Six Months That Changed the World (2003) by Margaret MacMillan, p. 33

Characters and Anecdotes book, 1771

Referencing Oscar Wilde from the preface of "The Picture of Dorian Gray"; "All art is quite useless".
1990s, Moab is My Washpot (autobiography, 1997)
Source: Moab Is My Washpot
Context: … but love, like all art, as Oscar said, it's quite useless. It is the useless things that make life worth living and that make life dangerous too: wine, love, art, beauty. Without them life is safe but not worth bothering with.

Variant: There is nothing so useless as doing efficiently that which should not be done at all.

Soliloquy on a Beauty in the Country; reported in Bartlett's Familiar Quotations, 10th ed. (1919).

Ibid., p. 279
The Book of Disquiet
Original: Porque é bela a arte? Porque é inútil. Porque é feia a vida? Porque é toda fins e propósitos e intenções.

Source: Goliath