he is talking about modern America after 1930s. If you talk to old generation Americans, without the social security system, old Americans still relied on
offsprings to support them financially.
before WWII, Americans usually had many kids for one family. Partially it was because birth control tech was not available, and partially because the death rate was high for young people and partially because of christian family value.
You can not just use mathematical models to explain anything.
from mathematical calculation, having kids in US is a negative NPV investment. But people here still enjoy doing that, even for very rich and highly educated families.
