To say “that feeling” of indignation (at the letter’s inclusion in a gallery) is the same as other things that make him roll his eyes, is reductionist. We regard things as stupid for different reasons; they’re not all the “same feeling.” As others have said, the artist’s intentionality in presenting something is part of its message. So the indignation he felt about a piece being put in a gallery is part of that piece’s effect on him, born from the artist’s choices. That feeling is different than hearing a moron say something dumb and thinking it’s stupid.

Intentionality is the key. Case in point, “language evolves” is a silly thing to say after a mistake, but many subcultures start misspelling things on purpose, and that intentionality is how language evolves.