If all student loans were privatized, people majoring in marketable degrees like nursing and engineering would be paying about 3%. People majoring in women's studies and similar fluff would be paying about 30%. The market would build in the risk of default according to the value of the degree and price the loans accordingly.
Also by privatizing loans deals can be worked out.
Being in hock for a student loan is worse than being in hock to the IRS. They never let you off the hook.