Right, so the issue with the income premium without economic growth argument is that the government would have collected those incomes anyway, just from different people (unless the student loans are structured as a % of future earnings, in which case I apologize for my ignorance).

Of course, degrees aren't zero value, but the subsidies for education (student loans) could still be distorting supply in a way that results in a net loss for the government. For example, a self-taught engineer or entrepreneur spends years in school instead of inventing or starting businesses. This is a poor allocation of investment and human capital which results in a net economic loss (including a loss for the government).