Sadness is certainly not a desired or attractive feeling with its dense cluster of synonyms that are difficult to separate with any precision (boredom, angst, depression). It never has been, even if it has had a certain consideration in literary and philosophical circles (think of Spleen, the meditative or melancholic sadness, of Romanticism and decadence, or of the angst of Heidegger as the cipher of human existence) and has, in general, influenced the entire history of culture and medical research in the West.
Starting after the Second World War, perhaps with the intention of leaving behind the horrors of what had happened, some sought to eliminate sadness and propose a vision of existence marked by perfect serenity. And yet sadness is a part of life and it helps us understand the richness of its subtleties; it also contains important lessons for living well. Trying to suppress sadness would be like trying to eliminate the night from the arc of a day. Eliminating sadness would mean preventing oneself from experiencing the emotions and attitudes that are its mirror-opposite, like joy, peace, creativity and enthusiasm for life.
Art reminds us of its necessity. One need only think of the play on chiaroscuro that, for example, characterizes Caravaggio’s Call of St. Matthew. When the dark colors are taken away (something that can easily be done by computer), the final effect is horrible; it becomes impossible to grasp the beauty and the dramatic depth of the depiction of the event that forever changed the life of that tax collector.