... a sufficiently high availability of unemployed, available, and in some cases desperate workers to permit the employers to consider workers expendable

Employers do, always have, and always will consider workers "expendable", whatever the state of the economy & the unemployment rate.

Like 'em or not, unions are the only thing standing between workers and exploitation- a lesson learned thru over a hundred years of struggle- a history that has largely been forgotten.

That's why we're re-living the Gilded Age & the reinstatement of conditions circa the turn of the last century.