Though most American youth continue to learn about sex most everywhere but in school, there is some good news: according to a recent report from the Sexuality Information and Education Council of the United States (SIECUS), the Obama administration and Congress in 2010 eliminated two thirds of federal funding for abstinence-only-until-marriage education, and, in a historic shift, allocated close to $190m for comprehensive sex education.

At the local level, New York Mayor Michael Bloomberg announced the implementation of a comprehensive citywide sex ed program this spring. Previously, whether a child received science-based sex ed or nothing at all was an enrollment roll of the dice: some principals ran good programs; others did not.

The proposed curriculum has sparked a rightwing backlash (flames fanned, in part, by the New York Post). Some parents are apparently angry that one approved website discusses pornography, swinger clubs and (dear Jesus) foot fetishes.

Bloomberg, for good policy and for ill, is a steamroller. But other cities lag far behind, including school districts that don't preach abstinence-only.

Last month, I reported that Philadelphia public schools utterly fail to provide comprehensive sex education. When students are taught what little they are about condoms, it rarely happens before high school. And by then, it's often too late: 15% of Philly teens lose their virginity before age 13. Pennsylvania state law includes only a vague requirement that students be educated about HIV/Aids prevention.

The Republican presidential candidates would like to keep it that way. They are stalwart critics of science-based and medically accurate sex education, and frequently demonstrate that they never received it.

Texas Governor Rick Perry, when asked by a reporter to cite research supporting his position (he presides over a state with the nation's fifth highest rate of teen pregnancy), would say only that "from my own personal life, abstinence works".

Governor George W Bush implemented abstinence-only in Texas, and after he moved to the White House, his successor, Perry, benefited from a big increase in federal abstinence-only funding. Texas, according to a recent story in the Austin Chronicle, has taken in $23.3m in federal abstinence-only funds in the past four years alone.

And it's not just Christian wishful thinking translated into public policy. Governor Perry's position on sex education is rather more cynical: he supported a vaccine for HPV touted by his former chief of staff, then working as a lobbyist for vaccine-maker Merck. The move prompted fierce accusations from evangelical Christians, including from GOP presidential rivals Michele Bachmann and Rick Santorum, that the vaccine encourages promiscuity.

The Republican need for remedial sex ed is widely apparent. Michele's husband, Marcus Bachmann, runs a clinic that has been accused of offering "cures" for homosexuality (a charge Bachmann denies); Newt Gingrich, searching for a clean slate like some inverted Henry VIII, philandered his way from Protestantism to the Catholic Church; Mitt Romney, in his role as bishop to Boston-area Mormons, tried to stop a woman from getting a life-saving abortion; Herman Cain now confronts sexual harassment charges; and poor Rick Santorum, a man who does not understand the difference between being gay and bestiality, has earned a comeuppance from columnist Dan Savage who rebranded his surname to mean "the frothy mixture of lube and fecal matter that is sometimes the by-product of anal sex".

Ignorance is no excuse. Neither is it blissful: Choosing the Best, a popular abstinence-only curriculum, compares people who have sex before marriage to chewed-up gum: it "isn't as appealing as when it is unwrapped and new". The South, beacon of Christian virtue, has, according to SIECUS, the highest concentration of abstinence-only education and also the riskiest teen sexual behavior.

Not that sexual illiteracy is limited to the political right: take Anthony Weiner. It's an American epidemic: a self-enforced Victorian morality play amid ubiquitous and crassly commercialised mass eroticism. The stakes of sexual ignorance extend far beyond preventing pregnancy and disease. Young people now frequently text ("sext") intimate self-portraits to romantic interests with very little understanding of the psychic and social damage that a sexually explicit photo gone viral can inflict. Instead of school districts teaching about the brave new world of sex and technology, however, prosecutors have threatened to charge the unfortunate and underage models under child pornography laws.

And this is about more than sex. As Dana Goldstein writes at the Nation, "a person's position on sex ed is a proxy for a deeper set of questions":

"whether or not one supports the changes in gender and economic norms that have brought women into the workplace, delayed the average age at marriage and allowed couples to experience sex without the burden of pregnancy, through the use of hormonal birth control."

And yet there's less and less time for such critical thinking in the classroom: health concerns are squeezed by religious fanaticism at one end, and corporate productivity measures at the other. As I reported in Salon, the high-stakes standardised testing regime has decreased time for everything from history to recess. Forget about sex. Though, to be sure, Americans haven't. While abstinence-only classes encourage students to take a "virginity pledge", an estimated 95% of Americans end up having premarital sex. It's time to make sure that sex is safe – and, perhaps, even fun.