Interesting discussion on a the Volokh Conspiracy blog prompted by a column, “In Defense of Usury” in the Wall Street Journal by Dean Karlan and Jonathan Zinman. 

Several of the commenters raised the challenge that nothwithstanding the authors’ conclusions, very high interest rates are still “immoral” and should be banned. But I don’t really follow the logic of the critique–if there are no externalities, and those that borrow are better off as a result, what exactly is the argument for why high interest rate loans are immoral and should be prohibited?