> In a free market economy, unemployment is a necessity

Perhaps a "necessity" in the sense that it's a necessary outcome of a system designed like that.

E.g., you build an engine according to the principles of thermodynamics in this universe, a necessary outcome is wasted heat. The engine would not work if you prohibited the waste; or it would become something else entirely (not a Carnot machine anymore, or whatever).

The trick is to figure out a system where the necessary outcomes are not very undesirable. Pretty hard to do that with the entire human society.