I would argue that any artists' work that seeks to bring light to an oppressed person's cause or plight is powerful in its own right. There is a good chance that those who face oppression are being silenced. Their voices are not being heard and the articulation of this condition is tantamount for all to understand and hear the cries of others' suffering. In this light, I believe that art which displays those who are oppressed is powerful because it brings to light that which is silenced or ignored. Indeed, the aspect of being able to generate a profit over the condition of another's suffering is compelling. However, I would not use that to discredit the art or its subject matter because it seeks to bring to sight that which has been invisible.
It's hard to generalize about artists, their subjects, or the effect artistic works may have on government policy or public consciousness. In certain instances, however, one may speculate with some accuracy.
One of the best known documentary photographers was a woman named Dorothea Lange. Her photographs from the 1930s of displaced farm families and migrant workers set a new standard for honest, hard hitting picture taking.
Her images are poignant and depressing, yet they show strength, perseverence and even nobility. They are not exploitative of down and out people, rather they are an artistically rendered record of a time and a place in recent American history, and they serve as a warning and a call to vigilance. They are testament to the human spirit and condition.
The plight of the people depicted did not go unnoticed, and individuals who would have otherwise fallen through the cracks of a collapsing economy are immortalized, and their images have been seared into the American consciousness.
Observe and judge for yourself in the link below.