When was this decided to be legal?

I've decided, in utter honesty, that internships should be illegal.
Now before I begin, let me make it clear that I love my internship: the work, my coworkers, the office, the 9 messages on my phone, the too many emails in my inbox, the other guy named Paul in the cubical across the isle from me, all the above. That being said, it should be illegal for me to continue doing this.
Why, you may ask? Well, let me tell you.
I get paid zero dollars to work here. My work is free of charge. In exchange, I receive experience and knowledge, not money. There is a problem with this statement: it is false. I am not getting paid zero dollars, I'm getting paid negative dollars. Non-paid internships are only possible if one is getting college credit for taking the internship. My tuition for college is roughly $30,000 a year. This tuition can be divided by the amount of semesters (2) and units I'm taking per semester (16) to become $937.50 per unit. My internship class counts as 4 units. I am, therefore, taking this class for $3,750. Before I continue, let me also say that my internship is 30 miles away from where I live. I intern 3 days a week and spend about $200 on gas a month with approximately 4 months per semester.
In conclusion, I am paying $4,550 to be working for free to gain experience. Does this seem like a logical means of gaining experience? Sweat Shop.
How is this legal? I'm still confused. I feel like a company can afford to pay me minimum wage. Or even if it was less than minimum wage. If there was an agreement that I would be working here for a semester and be paid $5 an hour, I'd be okay with that. But I'm getting paid negative $4,550. I feel like something is wrong here.