To emphasize only the beautiful seems to me to be like a mathematical system that only concerns itself with positive numbers.
I enjoyed attending many art history classes. I learned a great deal about modern art and its evolution (with a focus on American tradition) and the concept of style in painting from Molly Warnock, Filipe Pereda and Micheal Fried.
On modern art, and its necessity, I liked Ad Reinhardt essays. In short, his ideas are summarized in this painting.
Composition 8. V.Kandinsky