The economy is there to the benefit of the people in it, not the other way around. An ever-increasing number of people on this fixed sized planet is simply unsustainable.
If we can live with less people who are happier, what's not to like?
Indeed. Imagine having to lower real estate prices because demand falls. Fossil fuel use going down, less useless crap produced for less people, less pollution. Having to raise wages because of less unskilled labour available.
My counter argument is that humans are more wasteful when faced with abundance. Look at what we did when we discovered two continents worth of land. When perceived costs are low, waste is high.
It certainly seems like it would be a good thing for the economy, if you define "the economy" as how well all the humans are doing, as opposed to just absolute GDP and how wealthy the wealthy are.
If we can live with less people who are happier, what's not to like?