Yeah, but how many times have kids asked for advice here about how to get into the business and they've been advised to work for free (pushing cases, sweeping floors, etc.) just to get their foot in door and show that they are serious?
I have offered the above advice on many occasions, but it has never been with the understanding that someone, even a n00b, would work for free. A lower wage, or fewer benefits, yes, but work is work in my book and should be paid. Also, most of the time I have advised people to seek entry level employment opportunities through the IATSE call list in their area. No one on the IATSE payroll works for free. Period.
Free or volunteer work is what school is for (and maybe church). If you are working on a production in a professional environment, you should be paid, no matter what your level of experience is. Companies and job heads who say that you have to work for free to prove you are capable/worth keeping/serious about the work are the scum of the earth and promote nothing other than slavery.