Irrespective of whether JCcage was a con man or not, or his musical credentials, and despite my love for the grandest and loudest and most organized sound (thats why I love Mahler and Stravinsky and now Salonen), I gotta admit this about Cage: it took some guts to write a 'piece of music; where the pianist walks on the stage, sits in front of the piano for 4'33'' (btw this is 273 seconds, representing absolute zero in the Kelvin scale), then gets up and walks out. He was making a bold philosophical statement that makes us question who we are and how we relate to music from a broader perspective. So this is not really music but about us humans. It has its place in history and we cannot erase it.
No, we cannot ever erase the damage done by Cage and his ilk. Was it a bold philosophical statement or extreme laziness coupled with arrogance and a calculating understanding of just how gullible his audience really was?
I am reminded of the Gilbert & Sullivan operetta "Patience" which according to Wikipedia is "a satire on the aesthetic movement of the 1870s and 80s in England and, more broadly, on fads, superficiality, vanity, hypocrisy, and pretentiousness." I love Gilbert and Sullivan, and whenever I see "Patience" the leading character reminds me of John Cage. I highly recommend the experience.
During the late romantic era, the leading composers were Tchaikovsky, Dvorak, Brahms, and Verdi. Eventually, the value of the music composed by Bruckner, Mahler, Grieg, and a few others was recognized. But if you have ever listened to "Unsung Masterworks" on YouTube, you know that there are many, many more composers who were active in that era, composed diligently, and wrote often attractive music. They did not gain fame or lasting recognition. Why not? Is it just luck? Was it like Hollywood and they refused to go to bed with the most influential critics? Right now I am listening to Victor Bendix Symphony No. 3 (1895). A very enjoyable piece of music. Why is Brahms lauded and not Bendix?
The answer is that with enough hours, months, and years of study we can begin to glimpse the why. Music of value consists of melody (motives), harmony, counterpoint (voice leading), orchestration, form, structure, and artistic (aesthetic) content. Apparently, some admire the artistic or aesthetic content of John Cage's 4'33" but what about melody, harmony, counterpoint, etc. It is devoid of all other elements. A good melody, all by itself, would not be worthy of being called great music. But I think it would have a better claim to greatness than silence.
And despite Jerry's post above, I would say that Jerry's music has an infinitely better claim to greatness than anything ever put on paper by John Cage.