The triangle

Since my return, I had a lot of thoughts about the role of the viewer, the spectator, the "amateur d'art". It appears to me that in the triangle artist-work of art-viewer, the viewer's role is increasing recently. Academic art is art to be admired. Abstract art engages the viewer. He/she has to project himself/herself in the piece of art.

Is there art without a viewer?
The extreme is making art just to engage the viewer and "look at the reaction". This becomes the only purpose of art: to provoke the spectator who ultimately creates the message. At the theater, the actors stand motionless on the scene and the spectators reaction becomes the play. At the FIAC, I overheard an artist walking by, who had a heated discussion with another: "I just did this piece to see people's reaction ".
A painting becomes a mirror for the viewer.