The concept of maternal instinct had figured prominently in
scientific theories since the time of Charles Darwin. Late 19th-century
psychologists believed women possessed a unique need to create and care
for offspring. In the late 1800s, experts attempted to use biology to
shore up this theory, positing that maternal instinct was located in the
female reproductive organs.
Hollingworth wasn't buying it. "There
is no verifiable evidence to show that a maternal instinct exists in
women of such all-consuming strength and fervor as to impel them
voluntarily to seek the pain, danger, and exacting labor involved in
maintaining a high birth rate. We should expect, therefore, that those
in control of society would invent and employ devices for impelling
women to maintain [the] birth rate."
She believed the circulation of the myth was itself one of these
devices. Other ways society pressured women into having more children
included the promotion of the idea that only abnormal women don't want
babies; stigmatization of interests other than the maternal as
dangerous, melancholy, or degrading; female sterility as grounds for
divorce; limited education opportunities for women; and the widespread
depiction of the "sacredness and charm of motherhood" in art,
literature, and music.
Additionally, contraception was illegal and
considered obscene, and dissemination of any family planning
information was outlawed. Hollingworth was writing in the same year that
Margaret Sanger opened the first birth control clinic in the US, which
police immediately shut down.
https://broadly.vice.com/en_us/article/the-century-long-battle-to-disprove-the-myth-that-all-women-want-children?