Terez wrote: No one's got the philosophy written out as such - at least, not as it pertains to the entire music academy (others such as Schoenberg have written as much explicitly) - but you pick it up in the attitudes toward functional music among the academicians, especially functional music that was written in the 20th century.
Oh yes, I remember Schönberg states something like that explicitly ("emancipation of dissonance"). I just stumbled a bit about you saying "most of the 20th century", because I would think that Schönberg and the tradition he has started (Berg,Webern,Boulez,Stockhausen,...) is just one single "phenomenon" within 20th century music. I think many people have basically only the second Viennese school and its followers in mind when they read the term "20th century music". Which is sad. I would think that even a radical guy like John Cage would never have said that he prefered dissonant sounds (on the other hand, it seems that for him all things were equal anyway).
There's a large number of composers represented here at PS (Poulenc one of the more prominent examples) who obviously did not follow the philosophy of "more dissonance".
Ah, and regarding the pet hates, at this moment only one thing comes to my mind (but this is hate clearly):
-> Mahler symphonies (and basically most of the "late-romantic" symphonies, also Bruckner etc.)
More people in the orchestra do not make for better music.