The last time I saw Gail Dines speak, at a conference in Boston, she moved the audience to tears with her description of the problems caused by pornography, and provoked laughter with her sharp observations about pornographers themselves. Activists in the audience were newly inspired, and men at the event – many of whom had never viewed pornography as a problem before – queued up afterwards to pledge their support. The scene highlighted Dines's explosive charisma and the fact that, since the death of Andrea Dworkin, she has risen to that most difficult and interesting of public roles: the world's leading anti-pornography campaigner.

Dines is also a highly regarded academic and her new book, Pornland: How Porn Has Hijacked Our Sexuality, has just come out in the US, and is available online here. She wrote it primarily to educate people about what pornography today is really like, she says, and to banish any notion of it as benign titillation. "We are now bringing up a generation of boys on cruel, violent porn," she says, "and given what we know about how images affect people, this is going to have a profound influence on their sexuality, behaviour and attitudes towards women."

The book documents the recent history of porn, including the technological shifts that have made it accessible on mobile phones, videogames and laptops. According to Dines's research the prevalence of porn means that men are becoming desensitised to it, and are therefore seeking out ever harsher, more violent and degrading images. Even the porn industry is shocked by how much violence the fans want, she says; at the industry conferences that Dines attends, porn makers have increasingly been discussing the trend for more extreme practices. And the audience is getting younger. Market research conducted by internet providers found that the average age a boy first sees porn today is 11; a study from the University of Alberta found that one third of 13-year-old boys admitted viewing porn; and a survey published by Psychologies magazine in the UK last month found that a third of 14- to 16-year-olds had first seen sexual images online when they were 10 or younger – 81% of those polled looked at porn online at home, while 63% could easily access it on their mobile phones.

"I have found that the earlier men use porn," says Dines, "the more likely they are to have trouble developing close, intimate relationships with real women. Some of these men prefer porn to sex with an actual human being. They are bewildered, even angry, when real women don't want or enjoy porn sex."

Porn culture doesn't only affect men. It also changes "the way women and girls think about their bodies, their sexuality and their relationships," says Dines. "Every group that has fought for liberation understands that media images are part and parcel of the systematic dehumanisation of an oppressed group . . . The more porn images filter into mainstream culture, the more girls and women are stripped of full human status and reduced to sex objects. This has a terrible effect on girls' sexual identity because it robs them of their own sexual desire."

Images have now become so extreme that acts that were almost non-existent a decade ago have become commonplace. From studying thousands of porn films and images Dines found that the most popular acts depicted in internet porn include vaginal, oral and anal penetration by three or more men at the same time; double anal; double vaginal; a female gagging from having a penis thrust into her throat; and ejaculation in a woman's face, eyes and mouth.

"To think that so many men hate women to the degree that they can get aroused by such vile images is quite profound," says Dines. "Pornography is the perfect propaganda piece for patriarchy. In nothing else is their hatred of us quite as clear."

Born in Manchester, Dines moved to Israel in 1980, aged 22, and soon became involved in the women's movement. An event organised by the feminist consciousness-raising group Women against Pornography in Haifa – in which pornography was shown – changed her life forever. "I was astounded that men could either make such a thing or want to look at it," she says. From then on, she knew she had to campaign about the issue.

There were two images from Hustler magazine that she found especially shocking: a cartoon of a construction worker drilling a jackhammer into a woman's vagina, and one depicting a woman being fed through a meat grinder. "I was newly married and told my husband that night how appalled I was, which he fully understood," she says. "If he had said I was a prude I don't think I could have stayed with him."

The couple moved to the US in 1986, and Dines has taught at Wheelock College, Boston ever since, where she is professor of sociology and women's studies and chair of the American studies department. She is something of a lone voice in academia. Aside from what she says are "a handful" of colleagues across the US, most contemporary scholars are positive about pornography, and Dines thinks this is due to both a fear of being considered in alliance with the religious right and the view that pornography represents and champions sexual liberation.

"Many on the liberal left adopt a view that says pornographers are not businessmen but are simply there to unleash our sexuality from state-imposed constraints," she says. This view was reflected in the film The People vs Larry Flynt, where the billionaire pornographer of the film's title – the head of the Hustler empire – was portrayed as a man simply fighting for freedom of speech. Dines disputes these ideas. "Trust me," she says, "I have interviewed hundreds of pornographers and the only thing that gets them excited is profit."

As a result of her research, Dines believes that pornography is driving men to commit particular acts of violence towards women. "I am not saying that a man reads porn and goes out to rape," she says, "but what I do know is that porn gives permission to its consumers to treat women as they are treated in porn." In a recent study, 80% of men said that the one sex act they would most like to perform is to ejaculate on a woman's face; in 2007, a comment stream on the website Jezebel.com included a number of women who said that, on a first date, they had, to their surprise, experienced their sexual partner ejaculating on their faces without asking.

Sexual assault centres in US colleges have said that more women are reporting anal rape, which Dines attributes directly to the normalisation of such practices in pornography. "The more porn sexualises violence against women, the more it normalises and legitimises sexually abusive behaviour. Men learn about sex from porn, and in porn nothing is too painful or degrading for women." Dines also says that what she calls "childified porn" has significantly increased in popularity in recent years, with almost 14m internet searches for "teen sex" in 2006, an increase of more than 60% since 2004. There are legal sites that feature hardcore images of extremely young-looking women being penetrated by older men, with disclaimers stating all the models are 18 and over. Dines is clear that regular exposure to such material has an effect of breaking down the taboo about having sex with children.

She recently interviewed a number of men in prison who had committed rape against children. All were habitual users of child pornography. "What they said to me was they got bored with 'regular' porn and wanted something fresh. They were horrified at the idea of sex with a prepubescent child initially but within six months they had all raped a child."

What can we expect next from the industry? "Nobody knows, including pornographers," she says, "but they are all looking for something more extreme, more shocking." She recently interviewed a well-known pornographer, while his latest film played in the background. It contained a scene of a woman being anally penetrated while kneeling in a coffin.

In Dines's view, the best way to address the rise of internet pornography is to raise public awareness about its actual content, and name it as a public health issue by bringing together educators, health professionals, community activists, parents and anti-violence experts to create materials that educate the public. "Just as we had anti-smoking campaigns, we need an anti-porn campaign that alerts people to the individual and cultural harms it creates."

"Myths about those of us who hate pornography also need to be dispelled in order to gain more support from progressives," she says. "The assumption that if you are a woman who hates pornography you are against sex shows how successful the industry is at collapsing porn into sex." Would the critics of the employment practices and products at McDonald's be accused of being anti-eating, she asks pointedly.

The backlash against Dines and her work is well-documented. Various pro-porn activists post accusations about her on websites, suggesting she is motivated by money, hates sex, and victimises women to support her supposed anti-male ideology. Salon.com reported recently that the sex writer, Violet Blue, had launched a pro-porn campaign to counteract an anti-porn conference that Dines and colleagues held last month. Dines is regularly criticised by pornographers in the trade magazines and on porn websites and she tells me that her college receives letters after any public event at which she is speaking, attacking her views.

Does she ever feel depressed by all this? "It gets me down sometimes, of course. But I try to surround myself with good things – my students, colleagues, and my family." She says the blueprint for her aims is the eradication of slavery in the US, which was achieved despite the fact that every single institution was geared to uphold and perpetuate it. "What is at stake is the nature of the world that we live in," says Dines. "We have to wrestle it back."