I object to unpaid internships chiefly because they tend to reinforce privilege. The kid whose family is just getting by doesn't take unpaid internships--he's out working for pay, maybe coding, maybe waiting tables. The kid taking the unpaid internship is generally not getting a bad deal, for his or her family is willing to cover any loss of wages for kid's chance to shuffle papers of Sheryl Sandberg.

(Let me add that this is an objection on principle, not one of resentment; I never heard of such arrangements when I was of an age to be an intern.)