I think there's a value distinction to be drawn between boundary explorations that expand the art form and those that simply depart from any definition of it separate from the other arts. That leaves a broad scope for innovation: the composers of the ars subtilior, Carlo Gesualdo, Hector Berlioz, Debussy and Satie, Harry Partch, Antheil and Edgard Varese, and the progression of serialism from Schoenberg through Webern to Boulez — all of them explored and expanded the boundaries of music, but you can still experience their works as music, even if some have argued that it's bad music. It all can be, and has been, accepted as music.
But some of Cage's works (of those which he presented as musical) depart from musical material and musical experience to play with the nonmusical culture that surrounds music and musicians, or, abandoning that, the idea of performance itself. Obviously 4'33", with its formalities of opening and closing a piano, is an example of the former, but his lesser-known 0'00" runs simply, "In a situation provided with maximum amplification, perform a disciplined action." In that case, the performer is as justified in a disciplined soiling of their pants as any musical act. I refuse to countenance such wanking. (Cage was by no means alone in this, but he's probably the most famous.)
I'm glad to see that even academic composers seem to have retreated from this dissolution.