I feel like you’re using the word “fair” in an econ 101 sense, not in the way most people use it.

“The market reached equilibrium” with child labor and indentured servitude. Most people consider child labor unfair, so law/culture/customs changed how the market operates.

Even within the narrow definition of “fairness” in economics you still have externalities. This can become really tricky and require ethical considerations beyond a “pure math” problem.