In regard to the two letters criticizing John Cage, I counter with the following:
What objective grounds can we appeal to to support the claim that Bach, Mozart and Beethoven are the culmination of Western music?
Did not Werner Heisenberg in 1927 convincingly argue that the physical universe cannot be measured determinately and thus may just be chaotic and without structure?
Furthermore, in regard to the idea of a structured, orderly universe, I'll offer this observation from the philosopher David Hume:
"Custom is the great guide of human life. It is that principle alone which renders our experience useful to us, and makes us expect, for the future, a similar train of events with those which have appeared in the past. Without the influence of custom, we should be entirely ignorant of every matter of fact beyond what is immediately present to the memory and senses. We should never know how to adjust means to ends, or to employ our natural powers in the production of any effect. There would be an end at once of all action, as well as that of the chief part of speculation."