The only people that can afford to take an unpaid job are those that are already well-off enough to survive without pay. That means that there are careers where the only way to effectively break in to the industry is to be well-off in the first place.
This is a major problem in many industries, including film, advertising, fashion, music, and others. If your parents can pay for an apartment in Manhattan, congratulations, you can get your foot in the door. If not, tough luck, go find another job more suited to your lower-class life."