Beginning in the mid-2010s, significant discourse emerged within fan spaces such as Tumblr and Archive of Our Own (AO3) regarding the ethical implications of portraying taboo and abusive sexual content within shipping fanfiction. "Shipping"—the depiction of a romantic or sexual relationship between fictional characters—has long been a staple within fanfiction. The lack of censorship emerging from spaces such as AO3 allowed for the portrayal of disturbing or taboo dynamics within fan works, including incest, abuse, rape, and pedophilia.

Within fandom, discourse is divided between "anti-ship" and "pro-ship" camps, focusing primarily on the extent to which fictional works depicting such content affect real-world behavior and attitudes. Anti-shippers, referred to as "antis," take the view that fictional portrayals normalize harmful dynamics and behaviors and pose a particular threat to children. Fanfiction depicting underage characters in sexual contexts is characterized as child pornography by such antis. Pro-shippers oppose antis on a variety of stances, including opposition to censorship and the rejection of notions of fictional abuse affecting reality. Both anti- and pro-shippers draw from primarily LGBT fan communities and share similar demographics, although antis are generally younger, with the largest contingent in their early-to-mid teens.

The legality of fictional works depicting minors in sexual contexts varies greatly between jurisdictions. Many countries, including the United States, ban such material under obscenity laws, although this faces frequent legal opposition. Academic opposition to anti-shipping have described the movement as a moral panic or "faux activism". Antis have been criticized for equating fictional content with real-world sexual abuse, online harassment of pro-shippers, as well as the spread of moralistic and pathologizing attitudes towards kink and sexuality. The pro-shipper backlash has also faced criticism, primarily for minimizing other critiques of fan works by placing them under the label of anti-ship.

The term "shipping," derived from "relationshipping," initially emerged in the mid-1990s within the X-Files fandom to refer to the fan practice of supporting a hypothetical romantic relationship between the main protagonists, Fox Mulder and Dana Scully. Supporters of romance between the two characters titled themselves "shippers," seeing it as the inevitable resolution of the show's unresolved sexual tension. They were opposed within the fandom by "No-Romancers," who viewed the two characters' relationship as platonic friendship. Shippers often turned to fanfiction to depict romantic and sexual interactions between the characters, leading to contemporary fanfiction websites aligned with either camp. The term later broadened to include supporters of any fan pairing of fictional characters. Such dynamics paralleled far older romantic pairings depicted in slash fanfiction, a term first originating in the early 1970s Star Trek fandom. Even earlier examples of romantic fanfiction retroactively described as shipping include the 1914 novel Old Friends and New Fancies.

Many shippers become strongly emotionally invested in their preferred relationships, even when no such romantic relationship is portrayed in canon. Because of this, conflict can emerge in a fandom between proponents of different ships. This is exacerbated when there are multiple plausible partners for a particular character, such as within love triangles. By the early 2000s, anti-fans opposed to certain ships came to be known as "anti-shippers."

The emergence of Internet fan communities during the 1990s allowed for the proliferation of taboo fanfiction in an anonymous environment. Traditionally, erotica, homoerotic romance, and depictions of torture (most notably in "hurt-comfort" works) were carefully distributed only within small cliques interested in such works. In the 1990s, fanfiction proliferated on forums like Usenet, including erotic fanfiction; however, controversies about erotic fanfiction led to rules about warning for explicit content and an environment that dissuaded some authors from posting their works. Later on, large fan-work host websites, such as DeviantArt and FanFiction.Net, allowed the free spread of work without traditional gatekeeping or the risk of connection to their creators' offline identities. However, these websites still forced works to adhere to terms of service that allowed the fansites to remain profitable to advertisers. Fanfiction portraying graphic violence or explicit sexuality was subject to frequent censorship and removal, which fans called "purges." Some purged fanworks depicted abuse, torture, gore, rape, incest, necrophilia, pedophilia, or bestiality. Such taboo works usually have no specific basis in the source material, which is often originally marketed towards children and young adults.

In 2007, a pressure campaign to remove extreme sexual writings was launched by an American group named "Warriors for Innocence" against LiveJournal, the largest fan content host in the 2000s. Six Apart, the owners of LiveJournal, briefly removed around five hundred journals in response; this prompted widespread community outrage, and Six Apart apologized and reinstated much of the content over the following months. When LiveJournal was acquired by the Russian online media corporation SUP later in 2007, the site underwent a mass-scale removal of content considered explicit under Russian media laws, including many LGBT works. The "destruction of LiveJournal communities" and ongoing censorship from Fanfiction.net led to the creation of the Organization for Transformative Works and the Archive of Our Own (AO3), a nonprofit and advertisement-free hosting site for fanfiction. The gradual migration of much of the fanfiction community to AO3 allowed for the sharing of taboo works without censorship. AO3 implements a tagging system to allow authors to mark works containing triggering or upsetting content, although a work's tags can often double as advertisement. The microblogging service Tumblr also serves as a center for fan works, although explicit content was stymied by a ban on "not safe for work" material in 2018. Tumblr's unique system of post dissemination and tagging both allows for the discussion of social justice issues and intense conflict between different online fan communities. Tumblr discourse trends towards separate camps around specific viewpoints and identities, creating highly combative "contact zones" where rival factions debate issues.

Although "anti-shipper" can refer to anyone opposed to a specific pairing of characters, the term anti generally refers to opponents of fictional sexual content considered harmful. The question of whether "fiction affects reality" is a central point of dispute between antis and the opposing camp of pro-shippers. Antis generally believe that taboo or abusive sexual content within fiction directly influences the views and actions of those who consume it, with pro-shippers disagreeing with antis for a broad spectrum of reasons, ranging from a complete rejection of fictional media's influence on behavior to a defense of harmful sexual dynamics when properly depicted as abusive.

Samantha Aburime, a fandom researcher, described antis as "hybrids that exhibit traits of fans, anti-fans and anti-shippers." Although specific viewpoints vary significantly within the community, they generally share a number of core beliefs. Antis oppose depictions of rape and sexual abuse, describing them as harmful to sexual abuse survivors. Antis consider the opposed content harmful to minors and abuse victims, especially depictions of rape, incest, and pedophilia. Many antis criticize other tropes, such as power imbalances (including age gaps) in relationships and the perceived fetishization of homosexual relationships. Antis also argue that sexual content involving underage fictional characters is child pornography and that the dissemination of such works functions as a grooming tactic to normalize sexual relations between adults and children. Legal restrictions on such material varies greatly between different countries and jurisdictions. In the United States, where the Organization for Transformative Works is based, sexual material which includes fictional depictions of minors is prohibited under federal obscenity law, although such restrictions face frequent legal challenges.

Pro-shippers (also known as anti-antis), etymologically inverted from anti-shipper, believe that creating or consuming fiction which depicts harmful behavior does not itself function as an endorsement of such actions. Some pro-shippers believe that fictional works can affect societal attitudes towards sexuality when portrayed irresponsibly, but they align with the general movement's support of artistic free-expression and the continuation of adult content within fan spaces. Because most antis are teenagers, many pro-shippers consider the anti movement an attack on sexual content in general and an attempt to displace adult-oriented content from fan spaces.

Both antis and pro-shippers are largely LGBT, reflecting the fanfiction community as a whole—a 2013 survey conducted by fans revealed that only 38% of AO3 users surveyed were heterosexual, with more nonbinary users than men. The two groups are demographically similar in terms of racial, gender, and sexual identities and report similar rates of neurodiversity and survivorship of sexual abuse. However, antis are generally younger than pro-shippers, with the largest contingent in their early-to-mid teens.

Although antis generally claim to be motivated by a desire to protect minors and abuse victims rather than by opposition to shipping itself, academic scholarship generally analyzes the movement as a "ship war gone too far". Tensions over pairings between various characters within the television series Voltron: Legendary Defender led to a large-scale expansion of shipping discourse in fandom spaces. Opponents of the romantic pairing of the characters Keith and Shiro (although both characters were adults within the source material, Shiro was several years older than Keith) characterized that relationship as pedophilic in nature.

The actions of antis have been compared to censorship campaigns against LGBT works, as well as regulatory codes such as the Hays Code and Comics Code. Antis have been variously characterized by critics as a cult, harassment campaign, moral panic, or as an unintentional outgrowth of religious conservatism. Anti tactics have been described as appeals to emotionally charged buzzwords; pathologization of sexual deviance, especially kink; and reputational attacks: accusations of homophobia, pedophilia, or abuse to draw support from uninformed outsiders. The movement has been linked to the convergence of call-out culture and "faux activism" within online communities such as Tumblr. The strong emphasis on protecting minors within the anti movement has been described as stemming from broader moral attitudes towards protecting children and adolescents from inappropriate sexuality and maintaining childhood innocence. The anti movement may reflect a broader Generation Z discomfort with sexual material.

While many antis disavow more radical actions, the movement has been criticized for online harassment. Some antis spam gore, violent pornography, and pedophilic imagery to pro-shippers, AO3 volunteer staff, and content tags associated with taboo fan-works. The "baffling" tactic of intentional dissemination of imagery opposed by the movement has been described by fandom researcher Agnieszka Urbańczyk as a means to attack pro-shippers: "The goal of such actions seems to be marginalization of people who create it or enjoy it." Some antis publicly describe pro-shippers as advocates of pedophilia or sexual abuse, and ultimately as causing direct sexual harm to children. Antis have also been criticized for sending death threats to pro-shippers. In 2020, Hannibal screenwriter Bryan Fuller was faced with criticism and death threats from antis after expressing support for pro-shippers. The scholar Renee Ann Drouin, who experienced doxxing and death threats as a result of research she was undertaking related to Voltron fandom, expresses concern about the challenges these discourses pose to researchers.

Pro-shippers have been critiqued for minimizing valid critiques of fan works by labeling any critics of their works as antis. Anti-racist critiques of fanfiction are sometimes described as anti-ship by white fans, leading to an environment where these and other critiques are dismissed as "anti". The pro-ship or anti-anti camp has also been criticized for harassment from their side, including harassment of people raising these critiques. Additionally, the term "anti" itself has been critiqued for being sometimes vague or imprecise, as well as contributing to a lack of nuance in discourse over fanfiction.

• Feminist sex wars – Collective debates amongst feminists regarding sexuality
• Puriteen – Online neologism
• Real person fiction – Genre of fiction