Along these lines, it doesn't fit to equate unpaid internships to serfdom. Serfdom involves effectively permanent, near total servitude to a landowner for most aspects of life. You don't travel. You don't get educated. You don't have upside. You can't escape. You're screwed. An unpaid internship is not at all like this. Unpaid internships are not "essentially a form of serfdom".
If your labour has value then you can find work that pays you a rate for it (except for minimum wage - more about this shortly). You have the opportunity to expose yourself to experience by doing internships. If you don't have anything better to be doing, then it's a win-win situation for you and the person you're doing internship.
When I was young I worked in a computer assembly shop for basically no money. In the course of this work I plugged a power cable into a motherboard and fried it. I probably rubbed customers up the wrong way, and certainly did dumb things. My labour was worth less than nothing, and I was lucky to have the opportunity to be allowed near the place or customers.
As I became valuable I struck a private agreement with the owner and spent a summer working full-time, for which I was paid one gravis ultrasound ACE. I think I ended up better on the deal than the owner, but it was a close-run thing.
Another time I was contracted to do a job for an oil company. It took me a month to do something that would now take me a day, and the end result was so bad that they got no return on investment of the the AUD 300 they paid me for the job. Note that in the case of the oil company work, I already had most of a computer science degree, and so was more qualified than the average kind of person who lives on minimum wage and still near-worthless.
After spending some time working to build up my skills, I'm now happy with my career. I wouldn't be here except for working in situations where I was earning less than minimum wage, often with people giving my low money on the offchance I might not be incompetent.
The minimum wage is a horrible stain on a free society. It traps people with low skills out of work and cements them into an underclass that's much more difficult to break out of. It prevents business that are operating on the edge from continuing to operate. It's a classic example of do-gooders riding in and creating damage.
There is an argument in favour of minimum wage, and it's this: some people are too incompetent to be capable of standing up for themselves, and these people would be easy to take advantage of for malicious bosses, of which there are no shortage. The minimum wage is a blunt force mechanism that aims (and fails) to protect this set of people. The reason it fails is that in protecting low-wage employed people, it locks out people who are in a worse situation - unempployed.
It's a ridiculous solution that hurts the people it claims to represent. There are much better avenues that would be cheaper and have more positive effect on people: basic risk, valuation and business skills being taught in early high-school, television campaigns that encourage people to think about how their labour is used, what they could do to make themselves marketable. Mechanisms to get people speaking English more effectively. Lower taxation. Effective technical colleges.
The minimum wage system is a mechanism designed by the elite to allow that elite to paper over things and sleep at night pretending they're doing the right thing. It hurts the people it claims to protect.