Slower economic growth. Continued labor shortages. Lower life expectancy. Higher levels of divorce. More demand for social services, but less tax revenue to pay for it. A sharp and persistent decline in the number of Americans going to college — down by nearly a million since the start of the pandemic, according to newly released figures, and by nearly three million over the last decade — could alter American society for the worse, even as economic rival nations such as China vastly increase university enrollment, researchers who study this warn.