Should the ability to receive student loans be based upon the ability to pay them back?

Higher education is an investment. Sometimes you make a profit, sometimes you take a loss.

Example: The US is in great need of engineers, doctors, and other science related fields. The demand for these jobs is fairly high, allowing for those employed to find work to be able to pay back the loans. Many liberal arts degrees are not in as high a demand an/or don't provide as great a benefit to society afterwards. Or a degree in Medieval History. While I agree they are necessary to an extent, they are not equivalent to science degrees.