Supervisor David Chiu wants San Francisco to become the first American city to oppose any ban on sex-selection abortions. It apparently has not occurred to him why no other city has chosen to do so.

Journalist Mara Hvistendahl, author of “Unnatural Selection: Choosing Boys Over Girls, and the Consequences of a World Full of Men,” estimates that sex-selection abortions have “claimed over 160 million potential women and girls — in Asia alone.” Thus it is rather disturbing to watch one of the most liberal politicians in liberal San Francisco grandstand in defense of a practice that devalues — destroys, actually — girls.

In other communities, people think it is immoral for a woman to abort a fetus because of her — or his — gender. You can support the right to abortion, yet still cringe at the thought that some women choose to abort a girl because they want a boy.

Somehow self-styled feminists have twisted support for abortion rights so that it trumps women’s very right to exist. Chiu’s bill has four female co-authors — supervisors Jane Kim, Katy Tang, London Breed and Malia Cohen. Mayor Ed Lee is supposed to be the adult in City Hall. According to his office, he expects to sign the measure. Sometimes San Francisco can be so liberal that it’s illiberal.

Where does this resolution even come from?

“A coalition of Asian American and reproductive rights, health and justice organizations has formed to educate the public about the stereotyping inherent in sex-selective abortion bans, to condemn the rhetoric of ban advocates as deeply offensive and organize to defeat such discriminatory policies,” quoth the resolution. Activists contend that bans on sex-selection abortion, which have been passed in eight states, are designed to limit access to abortion, not gender-based feticide.

In a press release issued by the National Asian Pacific American Women’s Forum, Chiu said, “The rhetoric used by legislators advocating these measures is perpetuating racial stereotypes, is deeply offensive and can lead to the denial of health care services to women. No woman should ever be scrutinized by her doctor based on her racial or ethnic background, but that is exactly what a sex-selective abortion ban encourages.”

When we talked on the phone Thursday, Chiu told me, “There is no evidence that sex-selective abortions are happening in the United States. The legislative bans are based on racial stereotypes. We shouldn’t be passing laws that could potentially cause doctors to not provide care or consider turning women in to authorities for these laws.”

No evidence? In 2011, Sunita Puri, then a UCSF medical resident, published a study on sex-selection abortion; 65 Indian immigrant women participated in the study, and 24 said they had sought abortions because they were carrying girls. Common sense tells you it is happening among native and immigrant families, and among all ethnicities.

China is associated with female feticide because its one-child policy led many families to choose that their one child be a boy. India also has a high ratio of boys to girls, but the phenomenon also occurs in the Balkans and Armenia.

The National Asian Pacific American Women’s Forum contends that anti-sex-selection laws are based on racism, as it sets out to take on sex-selection “myths.” Such as Myth No. 2: “India and China are the only countries where male-biased sex ratios exist.” The problem is, the paper doesn’t identify who made that bogus claim.

I don’t support a legal ban on the practice. For one thing, women simply can lie about why they want an abortion; there really is no way to enforce such a law. China has outlawed sex-selection abortions — which proves bans don’t work.

Still, I do not understand why Chiu would make this an issue. Yes, Assemblywoman Shannon Grove, R-Bakersfield, introduced a bill to ban sex-selection abortions, but it died in its first committee by a 13-6 vote in May.

Grove notes that China, India, Australia and the United Kingdom have outlawed sex-selection abortions. “Are all these countries’ laws motivated by racism?”

I wondered if Chiu introduced his resolution to boost his profile as he runs for Assembly. Was he trying to outflank rival David Campos, also a left-hanging supervisor? He says no. Besides, Chiu cannot outflank Campos, who told me he will vote for the measure and expects it to pass. It’s all about abortion rights, Campos said, even though in this controversy they really are not under threat.

So why go out of your way to defend a practice that in Asia alone, Hvistendahl reported, has eliminated more women than the entire female population of the United States? Puri talked to immigrant women who aborted girls because their husbands or mothers-in-law wanted a male heir. Some feared that a daughter eventually would grow up to bring shame on the families. Women who delivered girls were subject to verbal and physical abuse.

Civil rights activists who rightly look at genocide with horror nonetheless suggest that San Francisco take a step back from condemning wholesale femicide. Soon San Franciscans will find out if City Hall is so afraid of offending politically active Asian women’s groups that it dismisses as racism any effort to curb a practice that aborts millions of little girls.

Debra J. Saunders is a San Francisco Chronicle columnist. E-mail: dsaunders@sfchronicle.com. Twitter: @DebraJSaunders