I understand if someone cold cases you for an internship and you cannot pay them but they want to learn and have some position in your company it's a bit more acceptable. But essentially if you send out job postings for interns you support a systematic evil in the job market of the US. These people have no choice but to work for you if they want to work in their field, and obviously no choice but to do so for free. You essentially try to write it off by saying it gives them value or experience but you as an employer are more interested in the free labor rather than what they derive out of it. There is no way around that. You aren't hiring them for their sake, you're hiring them because you get free labor that they are excited to do, and that's the best deal for you because you get the profit from it.
This hurts what people value their career at a critical juncture when they enter the job market. They see that everyone has to take unpaid internships meaning that companies aren't willing to value their work, this gets them thinking that their work is valueless. Which in turn is worse for any employer because the performance of the employee would suffer because of this diffusion of responsibility.
In short posted unpaid internships hurt the job market, hurt companies and most importantly hurt workers in their most critical time. Not only that but you seem to relish the opportunity of a person who is super excited to work on something for you for free, which is disrespectful of anyone you hire. I'm not against all unpaid internships, but most people see it as free labor, not altruistically training new employees for the job market. Even this article is prefaced with "Yay free labor in the summer!" which is what triggered my response, specifically this line: "I’m talking about internships - free, grunt work labor in the hopes of making connections and gaining a little bit of experience along the way."