100% agree with @ujjwal_sukheja here. As founders we should treat interns with the same level of respect like fixed employees. I got paid in all of my internships and felt incredibly motivated and empowered. If you want to attract and keep great minds: pay them, let them have real impact, and allow them to grow.
If we have people for less than 2 weeks, we just cover costs. They often wont be able to contribute much in that time, so the "exposure" seems (sort of) fair. Anything more than 2 weeks, they need to be paid a living wage IMO!
Of course they should! As a hirer you want the best possible candidate right? With unpaid internships you're self selecting for people who can afford to work for free as opposed to someone who might be the best possible candidate.