The foundation sent questionnaires to 821 sterilized former patients in 1926 asking how they were doing. The 173 letters they got back formed the basis of a report that concluded the overwhelming majority were satisfied with their new lives.
Only a handful of those letters survive.
"I do not believe I have been benefited mentally by the operation; perhaps my 'pride' still resents the thought," one man wrote. "I did not and do not quite understand the motive or 'purpose' for compulsory operation.... Hope you can realize my viewpoint."
"Doctor, if you write my son do not mention the sterilization operation to him as he does not know it was performed," wrote another patient's mother.
"I think such operations is just the finest thing there is for people that not mentally or physically healthy: not only for them, but for all those women who are bearing unwanted and uncared for children," one woman reported.
"It was all a mistake," wrote a man who had been sterilized at Stockton state hospital. "I would rather not be sterilized as I do not think there is the slightest danger of myself being responsible for any weak or feeble-minded children, and I shall ever bemoan the fact that I shall never have a son to bear my name, to take my place and to be a prop in my old age.
"My brother is at present a patient at Stockton.... He does not intend to ever marry and does not wish to be operated on and as his brother I hope you will please see to it that he is not."
Sterilization in the United States continued until the early 1970s. Its demise had begun during World War II, and the number of operations slowed in the 1950s. Scientific advances discredited the link between heredity and mental illness. New techniques for treating the mentally ill took hold. And the Nazi abuses drove sterilization promoters underground.
As Gosney wrote to a colleague in 1940: "We have little in this country to consider in [terms of] racial integrity. Germany is pushing that. We should steer clear of it lest we should be misunderstood."
Popenoe eventually abandoned sterilization, turning his attention to marriage and family counseling, which he had advocated since the 1920s. In the 1950s, he became one of America's best-known marriage counselors -- a pop psychology guru with best-selling books, a syndicated newspaper column, articles in Ladies' Home Journal and appearances on Art Linkletter's "House Party" television show.
What had been done in the name of human progress was all but forgotten.
UCLA's Robert Edgerton was a young researcher working for a state hospital in Pomona when he and a colleague interviewed 50 former mental patients. Their 1961 study tested the still popular assumption -- propagated by the Human Betterment Foundation decades before -- that sterilized patients accepted their operations as beneficial.
Edgerton found that only a fifth of those interviewed approved of the operation, and most of them were unmarried men who felt freed sexually.
Nearly all of the women were devastated. Many were abandoned by their families. Those who married generally didn't tell their husbands what had been done to them.
"They said they were going to remove my appendix," one woman told Edgerton. "I still don't know why they did that surgery to me. The sterilization wasn't for punishment, was it? Was it because there was something wrong with my mind?"
Said another: "I love kids. Sometimes now when I baby-sit, I hold the baby up to myself and I cry and I think to myself, 'Why was I ever sterilized?' "
Edgerton attended the funeral of one of his subjects a few months ago. He had an IQ of 52 and couldn't read or write. Yet he worked, accumulated a fair amount of money and had plenty of girlfriends. He also was bisexual.
Edgerton won't divulge the man's name, or those of the 14 other sterilization survivors he has kept in contact with for four decades as part of a long-term study of life after institutionalization.
All are older than 70. One woman attempted suicide. One is an active member of a church and delivers food to the needy. Another was married to man who dominated her every move for 20 years. After he died, Edgerton said, "she took off like a rocket," went to school, got a driver's license and joined a bridge and Scrabble club.
Her new friends don't know her secret.
"Of all the things they endured in the state institutions, what has stuck the longest and most painfully is their sterilization," Edgerton said of his subjects.
"This scar that they carry is just a symbol of that."
In 1999, Edgerton interviewed dozens of former mental patients as part of a class-action suit over a Canadian sterilization program. The government of Alberta, which sterilized mental patients from 1928 to 1972, eventually settled and agreed to pay $55 million.
That same year, the Swedish government agreed to pay $21,250 to each person it sterilized from 1941 to 1975.
"What could we do for those people who are still alive?" asked state Sen. Dede Alpert (D-San Diego), whose committee earlier this year renewed interest in California's effort to sterilize its way to a better society. "What should we do beyond ... issuing an apology?"