As my economics professors insisted, cost is determined by scarcity and demand.
In modern economics "fertility" has no very definite meaning.
But in spite of the relative economic displacement they all cause, free trade, outsourcing, and technological displacement all have a positive net effect on the economics of the planet.
The appeal to authority cannot be permitted in economics any more than in chemistry, physics or astronomy.
There is in existence a vast store of accumulated knowledge, and few, if any, departments of economics have been left quite unilluminated by the researches of former generations.