It's dependent on society as a whole. Together, we determine demand, minimum wages, the availability of spending cash, etc. So, he's right, but there are caveats - impediments, if you will. A logical focal point would be to analyze these impediments, unless the goal is to transform society away from the 'free market'.
For instance, if there are no limits to the accumulation of wealth by the rich, then more of the circulating money is bound to be in their hands, as has been the trend for decades. This equates to less spenders, and less production. Perhaps if the distribution of wealth stabilized (not necessarily made equal) then more spending cash would be available to the lower classes (the masses, mostly). But that's only a possibility - odds are these people will continue to be stripped of wealth via planned obsolescence, usury, and generally taking advantage of ignorance/greed.