Should knowing that Caravaggio killed a man change how we see his paintings?
Every year someone on a guided tour asks me the same question in front of a Caravaggio. In 1606 he killed Ranuccio Tomassoni in a fight in Rome and fled, and spent his last years on the run under a death sentence. People know this now; it is part of how the paintings are sold to them.
I restore panel paintings, mostly earlier than Caravaggio, but colleagues who have worked on his canvases talk about him as if he were a difficult patient. And the late works are full of severed heads. In the David with the Head of Goliath in the Borghese, the head of Goliath is widely read as a self-portrait. It is hard to stand in front of that painting and not think about the killing.
So my question is not the usual "separate the art from the artist", or not only that. It is: does the biography change what the painting is, or only what we bring to it? If Goliath's face is a confession, then the life is inside the work. If it is just a face, then the life is gossip that we use to make paintings more exciting.
I am not sure the debates about art and morality, which are mostly about whether a work's content is immoral, even cover this. A painting can be morally serious while its painter was a violent man. What should a viewer do with that?