Is evoking anger, or negative emotions, a purpose of art?
Prior to the 1930s or so, evoking anger or negative emotions was not the purpose of art. Art was pleasing and talent was respected.
When the communists began stealth jihad into our culture, art was one of the routes.
I believe it is described in the book "The Naked Communist" that one of the planks of communism is to get the culture to turn on itself. Visual art and music were intentionally composed to evoke anger and to dumb people down. Thus the rise of "artists" like Jackson Pollock.