What we really mean when we say “capitalism” is just people freely engaging in agreements together.

That is untrue.

Capitalism the private ownership of production. It's a set of behaviors and legal protections[state enforcement] that allow companies to be bought, sold, and owned. It's defined by a number of constituent elements: private property, profit motive, capital accumulation, competitive markets, commodification, and wage labor.

It is not synonymous with simple free association.