I usually agree with Sowell, but those states that raised minimum wage typically experienced an increase in employment. I haven't a clue where he gets the idea that it is reduced. The economy is dynamic, not static. When the consumer has more money, the consumer buys more. That means more goods and services are demanded, and people are hired to meet the demand. When wages drop, the reverse happens. There is a reduction in goods and services and layoffs happen to compensate for the reduction.
We saw a dramatic example of this in the 1950s and 1960s and the first half of the 1970s when wages slowly went up, and an explosion in the sales of consumer goods resulted. When wages crashed under Carter, we ended up with double digit inflation.
Sowell is completely wrong on that basic idea of economics.