You have the power to go and train in something useful and desirable. No one is stopping you. No one has a whip to your back to force to to the office every day. Equating internships with slavery is just nonsense. And an insult to the many millions of people throughout the world who are still actually enslaved today.
I'm not equating the suffering of slaves to the suffering of an intern at Harper's. But to argue that the reason one might not get paid for work is that their work is worthless to the market is the only "nonsense" here. My point is that there are plenty of examples throughout history where this is not a correct statement.
I've not read this entire thread, so I apologize if this has been covered by others but, don't you agree that compensation or "gain" can come in many forms? Not the least of which are knowledge, ability, future prospects and industry connections? It seems to me that this is what is received (ideally) in lieu of cash compensation.