Because its hard as fuck to get a job and an internship can very often lead to a paid position. I started as an intern at an independent production company and as soon as the head guy caught wind at my skills as a video editor I started getting paid. Two years later I'm cutting a reality show. Pay your dues people and kill it. (with that said I've done work for the head honcho of Razor and Tie and he's a huge dick.)
No. I hate this argument, because it guarantees nothing. "Pay your dues" and "kill it?" Please. You could be the best intern, doing mountains of extra work and the company still could not hire you. It is hard to get a job and internships look good on resumes (that's why I had a two year one, and it paid). No internship should not come without at least a stipend. I never accepted unpaid internships and no one should. It's disgraceful for a company to not invest in people that do as much work (sometimes more) than people on their payroll. And it's disrespectful.