The biggest arguments about validity are almost always about this subject: whether or not certain things are allowed to be included as suitable areas for artistic attention, and whether or not certain others can be left out. Peter Schmidt used to have a phrase: “ … to omit what no one else has thought of leaving out.“ In music, no one thought of leaving out the music.
Brian Eno: A year with swollen appendices. Brian Eno´s diary.
Faber and Faber, 1996, p. 374