The following correction was printed in the Guardian's Corrections and clarifications column, Tuesday 2 November 2010

A reader expressed doubts about the provenance of a figure for the estimated global worth of the pornography industry, mentioned in a feature as $96bn (£61bn) in 2006. As it said in the piece below – Men against porn, 26 October, page 10, G2 – this estimate appeared in a recent book, Pornland. To clarify: the book's author says the figure is drawn from a US-based website called Top Ten Reviews, adding: "These stats are used by most people in the field because of the absence of other reliable figures." The site, which features a range of data on the subject of internet and other pornography, does not cite the statistical authorities on which its global estimate is based.

It was in the cerebral setting of a university library that Matt McCormack Evans noticed how pornography was shaping his life. He was watching a female librarian stack books on shelves, stretching for the highest recess, when it occurred to him he "should look up some librarian-themed porn that evening," he says. "I remember making that mental note, and then catching myself."

McCormack Evans was about 20 at the time, and he had been using pornography regularly for a year or so, since starting university and having private access to a computer. At first, he didn't think this was a problem. It was something he did alone; no one had to know. The habit need never bleed beyond his student bedroom. Then he realised his male peers were using porn too, openly, frequently – almost celebrating it – and it started to make him feel uncomfortable.

He had glimpses of how it might influence their lives. There was the librarian moment; a flash of how porn might shift the way he responded to women in the real world. There was the moment he noticed a male friend struggling not to ask the stupid, inappropriate question about oral sex that had occurred to him when a female friend mentioned her sore throat.

McCormack Evans, a thoughtful, articulate young Londoner, was a philosophy student at Hull university, and he had never been part of a particularly laddish crowd, but he noticed that the "relatively well-rounded young men" he knew were changing. "They came to uni, got their first computer, were alone a lot, and everyone became much more laddish. It got to the point where someone groped a woman's bum in a club, and I completely flipped out."

McCormack Evans, now 22, has just co-founded an online project to get men talking about their use of porn. Other such projects have often come from a religious, conservative standpoint, but the Anti-Porn Men Project is grounded in feminist principles, in the notion that pornography is an important social issue, and has a bearing on violence perpetrated against women and wider inequalities. There are, so far, 10 other people who will be writing on the site, and the idea is to create a community, he says, "where people can share their experiences and problems, and find an alternative voice".

In setting up the site, McCormack Evans is one of the few men worldwide to publicly discuss pornography from a feminist perspective – positive about sex itself, open to the idea of people engaging in the widest range of consensual sex acts, but concerned about the industrialisation of sex and where this leads.

Perhaps the most prominent is Robert Jensen, a professor of journalism at the University of Texas at Austin, who in 2007 published the devastating book Getting Off: Pornography and the End of Masculinity. In this, he writes about the porn series Slut Bus, in which men drive around in a minivan with a video camera, ask a woman if she wants a ride, offer her money to have sex on camera – the woman always says yes – and then, when the deed is done and she leaves the van and reaches for the money, they drive off, "leaving her on the side of the road looking foolish . . . There are men who buy videos with that simple message: women are for sex," writes Jensen. "Women can be bought for sex. But in the end, women are not even worth paying for sex. They don't even deserve to be bought. They just deserve to be left on the side of the road, with post-adolescent boys laughing as they drive away."

Slut Bus also featured in the 2008 book Guyland, in which gender-studies scholar Michael Kimmel maps the social world of the 16- to 26-year-old US male. He talks to young men about such websites and finds that "about half had heard of them and visited them. They thought they were 'funny', 'silly', or 'stupid' but also 'kind of cool'." Later he writes that although the websites openly refer to their use of "models" in the films, "none of the guys I spoke with thought these were staged events; instead, they saw them as documentaries, as reasonable depictions of reality. And that's the problem. Because what this tells us is that the guys who watch these videos actually believe that women will have sex with strangers for money, even if they're not desperate."

Kimmel has been writing and lecturing on the subject of pornography for two decades: in 1990, he edited the anthology Men Confront Pornography. Back then, he tells me, a significant percentage of his undergraduate students "well over half the women, had never seen pornography, didn't really know what it was about. Now, they all know . . . What also strikes me is that young men seem utterly unapologetic about their porn use. It's like it's so ubiquitous – what's the problem? And they expect a similarly casual approach from their female friends."

Kimmel remains open-minded about pornography – what's needed is a much broader conversation about it, he says – but the picture he paints in Guyland is nonetheless troubling. "Pornotopia is the place where [young men] can get even," he writes, "where women get what they 'deserve' and the guys never have to be tested, or face rejection. And so the pornographic universe becomes a place of homosocial solace, a refuge from the harsh reality of a more gender equitable world than has ever existed. It's about anger at the loss of privilege – and an effort to restore men's unchallenged authority. And, it turns out, that anger is worse among younger men."

This is especially disturbing when you consider the studies that have shown that young men are often keen consumers of pornography (in a 2007 Swedish study, for instance, 92% of young men and 57% of young women aged between 15 and 18 had watched a porn film). It's also disturbing when you consider the amount of material available. It has been suggested that the porn industry is in trouble, that it's facing the problem of how to make money when there is so much free material around – and when so many people are releasing their own amateur footage. But there is no doubt the business is still a sizeable force. As Gail Dines writes in her book Pornland, published earlier this year, the worth of the global industry was estimated at $96bn (£61bn) in 2006, more than 13,000 films are released annually, and "there are 420m internet porn pages, 4.2m porn websites and 68m search engine requests for porn daily".

Michael Flood, an Australian sociologist at the University of Wollongong, is founding editor of the pro-feminist website XY and has done analyses of young people's exposure to pornography. He says there is direct data on an increase in exposure over the last decade, "and there are other obvious reasons to suspect this, including increases in access to the internet and in the devices one can use to look at porn – internet-enabled mobile phones, in particular."

Mention porn to people who came of age in the 60s and 70s, and it's often a byword for big-bushed centrefolds or videos of awkward encounters with unusually attentive plumbers. But more recently, porn "features" – films that nod to a plot – have been joined by "gonzo" material, which only depicts sex. Many of the most popular films have become harder and angrier, while focusing on a range of acts which, as McCormack Evans says, "have never really existed outside the porn industry".

Jensen started analysing pornography 15 years ago and says: "If you had told me then that there would be a common genre where a woman was penetrated by three men at once, I would have said, 'Oh, come on'. But I've now seen things I don't think even Andrea Dworkin could have imagined." Even ardent fans have acknowledged modern porn's brutal trajectory. In 1998, the pro-porn campaigner and performer Nina Hartley admitted "you're seeing more of these videos of women getting dragged on their faces, and spit [sic] on, and having their heads dunked in the toilet."

While an enormous amount has been written about how pornography affects women – particularly the terrible way in which they are sometimes treated within the industry – less has been written about how it affects men, which seems odd given that, as McCormack Evans says, pornography is a product predominantly "made by men, marketed by men, and consumed by a massive male majority".

One obvious problem for many porn users is the conflict between their stated belief in equality and respect for women, and the material they're watching in private. McCormack Evans says he used to exist in a "kind of double consciousness. For that half hour when I was watching porn I thought, 'This is separate from my life, it won't affect how I view the world.' But then I realised it did."

Jensen says he hears about this disjuncture "all the time. Men will say, I know the images I'm watching are in direct contradiction to my own stated values, but I just can't stop". McCormack Evans says porn-watchers can quickly descend into self-hatred. "They're sitting there afterwards, and there's an image left on the screen, and they look at themselves and think, 'I'm disgusting' . . . Then their daughter comes in, or their wife, or their girlfriend, and they've just been to Pilates, and the next day they start looking up Pilates porn, or something crazy like that, and they feel even worse. It can become quite self-destructive."

It can also leave porn consumers with sexual scripts and images they can't forget, and can't resist calling to mind during sex. Dines reflects this in Pornland, in her encounter with "Dan", who is worried about his sexual performance with women, and tells her: "I can't get the pictures of anal sex out of my head when having sex, and I am not really focusing on the girl but on the last anal scene I watched . . . I started looking at porn before I had sex, so porn is pretty much how I learned about sex."

Dan isn't the only young man who started viewing pornography long before he had any sexual experience – and he's also not unusual in finding it difficult to shake its influence. Dr Andrew Durham, a social worker who counsels children who have problems with their sexual behaviour, says he has encountered children as young as eight "who have got into a mess as a result of ideas from watching pornography. At that age, what they see is almost an endorsement of the behaviour, because they're watching images of adults [authority figures] doing something – although the watching tends to happen in secret, so they know it's wrong as well. But it's often a case at that age of see it, do it."

Durham isn't a pro-feminist writer or campaigner himself, but what he has learned seems to reflect the same views. "Pornography reinforces the wider media-led messages about the roles of men and women," he says, "and can also reinforce a particular attitude towards sex, an attitude that is devoid of trust, caring, and, in the worst cases, consent . . . They're learning that sex is what men and boys do to – rather than with – their partners."

Once young men reach maturity, their ability to negotiate what they're seeing will have developed, but Flood suggests some might still find their porn use "crippling, in the sense of being routinely frustrated that the sex they end up having doesn't look anything like porn. Of course, some young men will find partners who are keen participants in the practices found in pornography but others won't, so it's complicated."

I ask Flood whether he thinks pornography undermines intimacy between men and women. "I do," he says, "partly because pornography scripts are really not very much about intimacy; they're certainly not about the complex negotiations of desire that sex can often involve . . . Having said that, I know that for some couples sharing porn, or indeed producing porn, is part and parcel of their intimacy, and I think there are ways in which that can be ethical. But I think it's rare."

The anti-sexist educator and activist Jackson Katz, author of the 2006 book The Macho Paradox, suggests the porn industry has an obvious interest in undermining intimacy between men and women – if couples were to find sexual fulfillment together, the market would plummet. And this opposition to intimacy, says Jensen, helps explain why porn has become so cruel, degrading and humiliating – why, to quote Martin Amis, it has become "a parody of love" addressing itself "to love's opposites, which are hate and death".

The truth is, says Jensen, that because pornography consists of the same repetitive sexual acts, it needs some form of emotional content to succeed commercially. It's that which staves off the boredom. "Now, if pornography went towards emotion that was about mutuality, respect and egalitarian relationships," says Jensen, "then men wouldn't buy it, because they're using porn to avoid those aspects of sexuality. So the route to maximising market share involves including emotions that men are more willing to accept in a commercial sex relationship – anger, aggression and domination."

I ask whether he thinks the content of pornography could actually get worse. There are several ways the porn industry could go further, he says, but these might prove the final lines that the culture won't allow it to cross. One is the use of children. At the moment, many popular porn videos include young women of legal age dressed as schoolgirls, "so the line is already blurred," says Jensen, "but I think the routine use of obviously minor children in pornography is one place it could go . . . The other is overt violence – I mean guns, knives and fists. In terms of fetishism, pornography has already explored everything you could imagine that reinforces the domination/subordination dynamic. So I don't know. Overt racism? But how could it get more overt than it already is?"

One of the weirdest aspects of porn is that "it's never really satisfying," says McCormack Evans. "It doesn't meet men's sexual needs. It doesn't meet anyone's sexual needs." If porn doesn't even fulfil that basic promise, why aren't more people questioning it?

Jensen believes "the culture doesn't want to look at it. A lot of it simply has to do with the number of liberal-left men who use porn themselves and don't want to engage in self-critique . . . And when it comes to heterosexual women: do you really want to know what your boyfriend or husband is using? If your husband is masturbating to images of women being degraded, can you really believe it when he says, 'Oh, I don't think of you that way?'. Now that would be naive."

There's one other obvious problem. "It's all very well to say, 'Don't people realise what this is doing in the long-term?'" says Jensen. "But when you're in front of your computer, with – if I may be graphic – your penis in your hand, and you can reach orgasm within three minutes, how much are you really thinking about the long-term?"