Reducing the hours worked per week leads to a lower standard of living for the average worker

 Reducing the hours worked per week, all else being equal, would lead to a decrease in the aggregate supply of labor in the economy. This reduction in the available labor supply would then result in decreased aggregate productivity, as there would be fewer worker-hours contributing to the production of goods and services. [1][2]

The lower aggregate productivity would translate to a decrease in overall aggregate production in the economy. With a reduced supply of final goods and services, the average price level in the economy would rise, leading to higher consumer prices. [3][4]

Higher prices, combined with the initial reduction in worker-hours, would cause a decrease in the average real wage rates earned by workers. This reduction in real purchasing power would ultimately lead to a lower standard of living for the average worker in the economy. [5][6]

In summary, the free market theory of laissez-faire capitalism suggests that reducing the hours worked per week, all other factors constant, would set off a chain reaction of decreased labor supply, productivity, output, and real wages, culminating in a lower standard of living for workers. The self-correcting mechanisms of the free market are the best way to optimize economic outcomes for all.

Sources

1 Human Action, Third Revised Edition by Ludwig Von Mises

2 Capitalism by George Reisman

3 Man, Economy, and State with Power and Market, Scholar's Edition, by Murray Rothbard

4 A Theory of Socialism and Capitalism by Hans-Hermann Hoppe

5 Classical Economics by Murry Rothbard

6 Marxism/socialism, a sociopathic philosophy, conceived in gross error and ignorance, culminating in economic chaos, enslavement, terror, and mass murder by George Reisman

Or in other words:

when everything else is/stays equal, reducing the hours worked per week leads to decreased aggregate supply of labor, which leads to decreased aggregate productivity, which leads to decreased aggregate production, which leads to decreased aggregate supply, which leads to a higher average price level, which leads to reduced average real wage rates of the average worker, which leads to decreased standard of living for the average worker.