I'm sure there are plenty of stories of unpaid internships working out quite well, and that's great. I believe my view on unpaid internships stems partially from the fact that I had 3 internships and they were all paid, as well as several part-time paid jobs in college that could have been considered internships. While one internship didn't pay much above minimum wage, the other two were pretty competitive for my industry and one even provided a scholarship, housing assistance and paid for me to attend a conference as well. Having these helped me pay for college and allowed me to do internships in the first place, as I grew up in a rural area and lived away from home in cities for my last 2 internships.
A tiny, amazing cafe I visited during a trip to Ames, Iowa for my internship with Wilbur-Ellis.
Luckily my industry of choice is one that believes in paying its interns and I know of many great internship programs in the agriculture industry. For example, here's an internship job description for Dow AgroSciences. While I certainly realize that an internship that provides this much to the student requires a large commitment for the company, creating an excellent internship program will benefit the student with the experience they gain and the company in being able to cultivate the next generation of workers and find the best internships to hire on full-time after graduation. While none of my internships resulted directly in full-time jobs at the company because they were all either small companies or small departments within large companies, they still gave me valuable experience. When a company invests in paying their interns and ensuring that they provide a valuable experience to the interns, they are investing in the long term.