The "evils" of private loans, in short, are that they are not subject to federal support and guarantees as are Staffords and Grad Plus. Which means that you need to read the fine print very carefully when you get a private loan, to see what you're getting into, in terms of interest rate caplessness, repayment terms, (lack of) deferrals, forbearance during residency, etc. Private loans are available because the lender can profit from you during the loan. Federal loans are considerably less profitable (and less risky) to the lender.