It depends on the value the intern provides vs. the value the intern receives. In general, I think it's better for interns to receive some pay but money is not the only thing of value an internship can (or should) provide.
I've only been alive a few decades and I've seen the corporations convert "entry level jobs" into "internships" in that timespan. So it is exploitative and it is a form of slave labor.
Of course not. But unpaid internship is always exploitation.
"Managers are assholes" is not very valuable information, you can pick that up from sitcoms and Dilbert. But you can learn a lot from bad jobs and the mistakes of others, including managers.
The "managers are assholes" bit was meant as a joke, and I learned loads from that internship. It's just that when you're that young and self centered, you tend to see what you didn't get rather than what you did.