There's a reason it's called a punchline. At the Edinburgh comedy festival there are rape jokes and domestic violence jokes bouncing through the town. It is strange why comedy, theoretically so revolutionary, should embrace the bloodiest kind of social reaction, but it is so.

I watched a young, gangly comic called Chris Turner position himself as a nerd, boast he went to Oxford University, and tell jokes about Roman numerals. Then it came: "I was waiting for my girlfriend to come round. Because I'd hit her really hard." Afterwards I asked him – why tell jokes about domestic violence? "Because it's funny," he said. "It's funny enough." Then he said he has studied feminism. So this is a culture that mocks the degradation of women; it is, as they say, only material and sometimes promotion. There is a show called Sex Tourist by Chris Dangerfield, which has a flyer you can take to an escort agency for £10 off.

Misogyny is a constant in standup, and has been for 20 years, since the feminist revolution began to crawl away from mainstream culture, to be shagged by Loaded. A comic called Gerry K tells a joke about watching a pimp fighting with two prostitutes. "I'm not having that," he says, "So I joined in." Here comes the reveal – "I punched her spark out." A comic called Paul Revill says: "Some audiences say they don't like rape jokes. They say that, but I know what they mean."

All this normalises and diminishes violence towards women: if it is easy to laugh about, it is hard to take seriously. There is an obvious connection between misogynist discourse and violence because, as Maureen Younger of Laughing Cows says, "Women are always the butt of these jokes. It's never the perpetrator". In these gaudy rooms, the indifference amazes.

It is most common on the open mic circuit where young comedians play for nothing and you can, if you wish, hear 20 comedians telling 20 rape jokes in one night. The comic Nick Page says: "It is getting worse because of the volume of people trying to enter the comedy industry without the life experience to create good jokes and good stories." Page was due to appear at an Edinburgh showcase last week, but he left after watching "three comics in a row doing rape or violence material. They were damaging comedy. But with the death of feminism in mainstream culture more and more people are prepared to put up with it."

It's true; even comedians that don't do misogynist material are protective of those that do, because they are wary of censorship and contemptuous of hecklers. When Daniel Tosh was told by a female punter that "rape jokes are never funny" he asked the audience, "Wouldn't it be funny if that girl got raped by, like, five guys right now? Like right now? What if a bunch of guys just raped her …" Other comics defended him and the promoter said: "You start dishing out something to a comic and try to be funny, you better be able to take it."

The comedian Sarah Bennetto told a story earlier this year about a comic she heard in one of the "horrible open mic hate filled rooms." The nameless man is the "perennial open mic act – frustrated and angry at the world, he blames women, minorities, everything for his lack of success". He was talking about how his female friend cried on his shoulder and so, he says, "I fucked her in the arse. I thought I'd really give her something to cry on my shoulder about." Then he said he might "slit her throat from behind, dig a hole in my back garden and bury her". This is not comedy, of course, but rage disguised as comedy. When the comic heard about Bennetto's anger he threatened her online, which is quite odd. She could have reasonably used the "irony" defence. I sort of wish she had. It would have been ironic.

But this is not a childish tic of the beginner. Famous comics do it and it makes them rich. Jimmy Carr has many rape jokes: "What do nine out of 10 people enjoy? Gang rape." What is rape anyway, he asks, but "surprise sex"? Russell Brand has called the police from the stage to say he had spotted a sex attacker. This giggling over sexual assault leaks all over Brand; according to the Sun, a few weeks ago, he held up shooting on a film set for two hours until the wardrobe girl showed him her breasts, and he should have been fired. Unfortunately, the only disciplinary action was from his co-star Billy Connolly.

Spiky Mike, who runs the comedy promoter Funhouse, says, "the comedians at the lower end of the scale follow what is in vogue at the top end. They see Jimmy Carr and Frankie Boyle doing extremely offensive material, try to copy it and do it badly, which is even more offensive".

I am not sure that a lucrative career in rape gags is more helpful than a failed one, but the rape hum seems eternal. And why not? As the US comedian Sarah Silverman says: "Who is going to complain about rape jokes? Rape victims? They barely even report rape."

Twitter: @TanyaGold1

• This article was updated on 18 August to clarify that information about Brand holding up shooting was reported by the Sun newspaper.