Sure, there is a minimum cost to a degree that may or may not line up with its earning potential... but $100K? How in the world do schools get away with charging that much for a degree whose earning potential is so low?
This whole problem would be a lot less of an issue if degrees cost proportionally (or at least roughly proportionally) to their market value. People who want to study "useless" degrees can do so, and their costs would be likewise much lower than people who want "useful" degrees for employment. Perhaps we'd all be better off as a society this way.