>For a scientist doing a ML system to reconstruct pixelated faces, trained with white faces, why is he/she responsible for "insert larger problem" outside of her/his field?

Because we're all responsible for how the tools we built are used and what they enable, and how they affect society at large. That's what ethics is about, something which seems to be absent in the education of the modern citizen and in particular engineer or scientist, who is supposed to come to work, program things and not think too much about the impact their products have on the world.