Mr. Lepant, I have to disagree with you here. You're assuming that money is the only form of payment, but as stated in the article, many interns value the free-to-them education that comes with working in a professional environment. There is value in learning how successful people function. Internships are supposed to be like apprenticeships; both sides benefit at minimal expense to both.
Above all else, however, it shouldn't be illegal to offer unpaid internships. These aren't slaves we're talking about; these would be free people making the conscious choice to accept a job in exchange for learning the workings of their chosen profession first-hand, rather than in exchange for money.