Stopes was a prominent campaigner for the implementation of policies inspired by eugenics, then not a discredited science. In her
Radiant Motherhood (1920) she called for the "sterilisation of those totally unfit for parenthood [to] be made an immediate possibility, indeed made compulsory."
She contributed a chapter manifesto to
The Control of Parenthood (1920), comprising a sort of manifesto for her circle of Eugenicists, arguing for a "utopia" to be achieved through "racial purification":
Those who are grown up in the present active generations, the matured and hardened, with all their weaknesses and flaws, cannot do very much, though they may do something with themselves. They can, however, study the conditions under which they came into being, discover where lie the chief sources of defect, and eliminate those sources of defect from the coming generation so as to remove from those who are still to be born the needless burdens the race has carried.
However, in this tract, she argues that the leading causes of "racial degeneration" are "overcrowding" and sexually transmitted disease (ibid, p. 211). It concludes somewhat vaguely, that racial consciousness needs to be increased so that, "women of all classes [may] have the fear and dread of undesired maternity removed from them ..." to usher in the promised utopia, described throughout. (ibid, p. 221)
She also bemoaned the abolition of child labour for the lower classes:
"Crushed by the burden of taxation which they have not the resources to meet and to provide for children also: crushed by the national cost of the too numerous children of those who do not contribute to the public funds by taxation, yet who recklessly bring forth from an inferior stock individuals who are not self-supporting, the middle and superior artisan classes have, without perceiving it, come almost to take the position of that ancient slave population."
In 1935 Stopes attended the International Congress for Population Science in Berlin, held under the Nazi regime. She was more than once accused of being anti-Semitic by other pioneers of the birth control movement such as Havelock Ellis.
As came to public attention years later, she was a personal as well as political devotee of Adolf Hitler:
“Dear Herr Hitler, Love is the greatest thing in the world: so will you accept from me these (poems) that you may allow the young people of your nation to have them?” These gushing words from an ardent fan (she was lucky Unity Mitford did not scratch her eyes out) were written in August 1939, just a month before this country went to war with Nazi Germany, by Marie Stopes [...]
After her son Harry married a myopic woman, Stopes cut him out of her will. The daughter-in-law—Mary Eyre Wallis, later Mary Stopes-Roe—was the daughter of the noted engineer Barnes Wallis. Stopes reasoned that prospective grandchildren might inherit the condition.
Supporters of Stopes generally concede that she made such remarks, but argue that they should be read in their historical context.
Following the death of Marie Stopes in 1958, a large part of her personal fortune went to the Eugenics Society.