We have minimum wage laws because we as a society have decided that some wages are too low to be just. "It's a volunteer position" exploits a loophole in that.
There are plenty of things like this in labor law, like mandatory breaks of a certain length after working for a certain amount of time. We recognize that the employer usually has much more negotiating power in the relationship with the employee, and try to equalize things a bit.
> You are not going to escape the fundamental fact that there are people who are out there wanting to work, but who cannot command the pay rate dictated.
Pay is only dictated by what people want or can command when demand for a certain kind of worker is higher than the supply. In this case, there appears to be more supply than demand, so the pay is determined by the perceived value the employer gets from the work. Given that this production presumably couldn't happen at all unless they filled these positions, the value of this work is greater than zero. So they should be paid for the work. The only reason they are offering zero pay is because there are people desperate for work, who will buy the (nearly-always false) representation that they'll get enough "exposure" or "experience" for it to be worthwhile.
IMO these sorts of predatory practices should be illegal, but it's really hard to do that without also making legitimate volunteer opportunities illegal as well.