Diego Rivera was a prominent Mexican painter. He rose to fame as part of the government-sponsored Mexican mural program, which sought to reclaim national identity and stir pride in native Mexican culture. His art is narrative and extremely political. 
The book, Siqueiros: his life and works, by Philip Stein (ISBN 0717807061, pp176) describes the following:
In 1948, in response to a controversy regarding his mural, Dreams of a Sunday in the Alamdea, which portrayed Ignacio Ramírez holding a sign reading, "God does not exist" (which he refused to remove from the mural), Rivera responded: "I am an atheist and I consider religions to be a form of collective neurosis. I am not an enemy of the Catholics, as I am not an enemy of the tuberculars, the myopic or the paralytics; you cannot be an enemy of the sick, only their good friend in order to help them cure themselves."