It would theoretically lead to a lower default rate, as it would dissuade "art history" majors from pursuing that low-paying profession. As it stands now, the people who pursue higher paying majors are subsidizing those who pursue the lower paying majors. You can't seriously say that an engineering major is the same risk as an art history major. Then why should they pay the same interest rate? You aren't going to claim that everyone should pay the same mortgage rate, right?