First off, the value proposition: Cuban is clearly intensely interested in getting this done, because it might be valuable to his company someday. Paraphrased, his argument is that it's not guaranteed to be valuable today, so he shouldn't have to pay anyone to do it. He wants the value, but he doesn't want to pay for it. That's exploitation, no matter how much he tries to sugar-coat it.

Second, the notion of "experience" being valuable: if it's true that the work being offered is worthless to Mark Cuban's company, then the intern isn't working for the Dallas Mavericks. She's at best doing something tangentially related to the Mavericks, and hoping that Mark Cuban or his organization will give her a good recommendation someday for doing it. The value proposition to the intern is, at best, debatable, and worse, the intern is in a position where she must excel in an unpaid position to gain any value at all. The best you can say about it is that it's ethically slimy.

Third, internships have inherent value to the employer -- they're extended interviews for paying jobs. That's why so many tech companies pay summer salaries and perks to college kids; they want to recruit good employees, cheaply. Cuban completely disregards this notion.

Fourth, Cuban grants that the internship has some probability of value to the Mavericks. Thus, the internship has some expected value to the organization. Cuban's argument that the internship has no value is just wrong. Companies routinely hire interns with no concrete expectations about their productivity, because the expectation of value is higher than the cost of a few interns. I'm highly skeptical of any counterargument that this wouldn't also be the case for the Dallas Mavericks.

In short, there are any number of logical holes in Cuban's argument, but the HN conversation is featuring a conversation about sex and individual liberty instead of discussing the topic at hand.