I guess it is postmodernist plague, where nothing has value and everything is relative. So people will just swallow the idea that everybody can be everything, and everything is everything. And nothing means anything anymore. Just give up in front of potential danger of brainwork and surrender in front of pranks.
The lame doodle is masterpiece, sound of distortion box is great noise album, etc.... But you can make critical evaluation = opinion based on something beyond mere gut feeling. You can value piece of creativity. If the artist or his followers can't take criticism, it's whole another issue.
Simple proof could be, that talking about book reference: When editor compiled book of avantgarde art - he makes the choices. He values what is worth of inclusion and what is not. Which works are good and which are shit. It would be utterly strange idea that you can't value avantgarde art!? Wouldn't this mean, every book is just compilation of whatever shit someone happened to make? But no. There is most often editor who compiles the essential and leaves out the shit. He/she is probably not afraid to make judgement or hide under idea that "everything is subjective", "nothing has value"...
This doesn't remove the possibility, that someone will always actually prefer the junk and gutter-trash, instead of "remarkable art", hah... Both trash and art is not beyond possibilities of finding value.
Often, the body of work, is important factor defining value. The doodle or black square itself may not have value, but its context in whole body of work and legacy of artist. His meaning in his time or in future.
In this angle, for example some works of David Jackman, are utterly useless. But those recordings in his discography together with other works create what IS Jackman.
One torn newspaper page with muddy footprint found from street is not remarkable art. But artistic intent, concept stretched beyond the mundane, may become so if it is well done. How can it be "well done", someone asks? I'd rather not take this discussion here. It may happen in "art section" if someone is into concept art?