Abstinence

The most unnatural of all the sexual perversions. Abstinence is the practice of refraining (voluntarily or involuntarily) from having sexual relations with other people. In stricter cases, abstinence also refers to not even masturbating. It should not be confused with celibacy, which is abstinence that is intentionally pursued for spiritual, philosophical, or moral motivations.

Birth control
When people attempting abstinence as birth control find their sex drive is too strong, this can result in unprotected sex or masturbation, especially if they put themselves in situations in which the temptation is likely to be strong. Despite its possible effectiveness, abstinence is highly unpopular in the United States and has been so since at least the 1940s.

Evangelicals like to say that abstinence is one hundred percent effective at preventing pregnancy. But when talking about birth control, we distinguish between perfect-use failure rates and typical-use failure rates. The former assumes the method is used correctly, while the latter is the actual rate at which women get pregnant while using the method. Thus, if a hundred women use male latex condoms, for example, eighteen will be pregnant within a year on average, while if they all use it perfectly, two will be pregnant. Typical-use failure rates are important, because human error is a thing. If abstinence is a birth control method, the same standard should apply; its effectiveness should be judged on how many women using it become pregnant. No data is available on this, but it happens often enough that any adult with non-zero life experience can see clearly that the typical-use failure rate for abstinence is a good deal higher than zero.

According to the Bible, abstinence is only 99.9999999999999% effective.

Abstinence programs
These programs are so-called "sexual education" courses for public schools which either emphasize abstinence in preference to proven sex education techniques, or in "abstinence only" programs, teach nothing else. It goes without saying that all studies show abstinence only programs are less effective than actual information on birth control and sexual health.

Other reasons for abstinence
A small but significant number of people quite voluntarily choose abstinence for any number of reasons.

Young people may choose to be abstinent if they don't feel that they're ready for sex yet, or if they haven't found someone they'd like to have sex with yet. Which makes a lot of sense; sex is complicated and there's a lot of wisdom in waiting if you're not ready.

Asexual people are generally abstinent (as they're not sexually attracted), but an allosexual may agree to abstinence to satisfy their asexual partner, especially if they are sex-repulsed (though it's worth noting that asexual people can have sex and masturbate if they'd like to, and that many asexual people do desire romance). Even people who are not asexual may just not find it not worth the risks (from STDs or similar) and difficulty navigating the dynamics of a sexual relationship, and even when available (legally or otherwise) aren't willing and/or able to pay someone for the experience.

Disability and mental health may play a role in choosing abstinence. The autistic woman who has serious sensory issues and struggles to relate to others, chose to forgo sex and romance of any kind in order to make her life simpler. (She also says she never had much interest in the first place. ) And people who have undergone trauma, especially sexual trauma, may decide that they're happier abstaining for now.

Abstinence and western religions
Western religions, thriving on control and demonization of sexuality in general, often "require" abstinence of their unmarried followers — especially those followers with a womb. Women were traditionally expected to go into the marriage bed a virgin. Even today, when sex out of wedlock is "okay", the amount of sex a woman has had prior to her wedding day is often considered in defining her character. "Good girls don't", don'cha know. These religions also teach fapstinence (abstention from masturbation).

As part of the "Culture War", this obsession with abstinence has not only resulted in abstinence based sex-ed programs, but in such unique events as "father-daughter Abstinence balls", abstinence clubs in schools, and virginity pledges. It's not as if none of them ever follow through, but really... you'd think that people would eventually realize that trying to keep teenagers from having sex is a completely syphilic Sisyphean task.

Sexual repression
There is some suggestion in scientific literature that prolonged abstinence might lead to sexual repression, which in turn risks causing aggression and violence as well as preoccupation with sex. The argument is that people who struggle to suppress their own sex drives become preoccupied with sex. This is ironic, considering that such people within religious organizations like the Catholic Church often seek to impose abstinence onto other people.

To be fair, the fact that the buildup of sexual frustration makes one kinkier could be seen as a point in abstinence's defense, as most religious institutions these days say that once actually married, one is free (and in non-fundamentalist Islam, outright encouraged) to get as frisky as they dang well please.