There were no laws restricting the showing of child porn in Denmark up until 1980.
There is no film censorship in the U.S., either. The MPAA rating system is a voluntary industry-supported system that provides viewers with information, but does not restrict what producers can put in their films.
I believe that some theaters and chains do not show NC-17 (an official MPAA trademarked rating) or X (not an official rating) films, which is how films with the content you describe would almost certainly be rated. But that is a matter of company policy, presumably because they prefer to be seen as “family-friendly.” That is not censorship, that is the market working.
The harsh criticism that the type of films you describe would receive from all segments of society means that they would remain deeply underground in most civilized countries. No government censorship would be needed, and it would probably be counter-productive, increasing the level of interest because of the Streisand effect.
Which is not the same thing as what you put in the thread title. And as far as this, nor in the USA until 1976, and that first ban was only on distribution and sale.
What they said. There is no proper “official” film censorship in the USA, producers have in-house “censors” (“standards and practices” departments) to avoid troublesome material but that’s a private matter.
You could not get legit financing and distribution for what is described in the USA, or Denmark. (Also, in the USA, at least, there are laws against profiting from portrayal or recount of your crimes, if convicted – and the film itself would be evidence since the actions themselves are crimes.)
However, as was brought up a few years ago during the big Islamic State in Iraq and Syria media campaign, it is not illegal per se to show a recording of an actual murder or other crime or atrocity. The material would be at the very least demonetized and search-blocked, and most likely purged from the site and the info as to who uploaded it reported to authorities.
I have actually known quite a few people who owned a copy of “Animal Farm” on VHS/Betamax video back in the day, a Danish film featuring copulation between humans and animals. Bestiality, as this practice is known, was never outlawed in Denmark up until 2015, so there would have been no restrictions on the sale of this stomach churning porno movie over there at the time. The lack of censorship would have allowed its free distribution. It was apparently smuggled into England through Customs in the early eighties. I also have a friend who was in the army, during the early seventies, I think, and saw animal sex films while stationed in Germany, another country where censorship is lax to say the very least.
I would say the American equivalent is that it’s not illegal in this country to buy a car. But if you kill somebody in order to obtain the money to buy the car, you’ll be arrested.
So I would assume if a Dane made a film depicting rape, murder, or torture, they would be arrested - for committing (or being an accessory to) rape, murder, and torture. The film would not be illegal in itself but it would be evidence of the crimes that had been committed.
In Ontario Canada Damaged Goods a film about sexually transmitted infection was banned in 1916. Canada has strong censorship laws.
A mainstream US film released in the 70’s called “Deep Throat” is believed by some to contain scenes of actual rape because its primary star, Linda Lovelace, claimed to have been forced to act in it at gunpoint by her ex-husband. However, this has never been proven and the only grounds the film has ever been banned on anywhere is containing scenes of actual sex, not rape.
In 2000 it was released uncut here in the UK when the restrictions on “hard-core” pornography were finally lifted.
I don’t think laws that existed in 1916 are likely to be relevant to this thread; at least unless you have a cite that they’re both still on the books and still enforced.
I’m not so sure about this. Plenty of gore and death scenes are shown on various sub-Reddits although they are videos from cell phones and Ring cameras, not professional done. Things like, “Man loses hand in motorcycle accident” or “Parachute does not open”. Some comments are subdued but there are many people who say things like, :“Man that thud at the end was sick!” or, “Gotta hand it to him…”
How many people sought out uncut videos of heads being cut off by terrorists? A long time ago I came across a site that featured actual photos of automobile accident victims. Very disturbing. One look was all I needed, I never went back… I don’'t know how police and EMTs deal with that level of carnage.
For some particular values of “mainstream”. 
I think there’s an additional modifier missing there.
Actually, no. It was reviewed by Roger Ebert and Variety, among others. Here’s what Wikipedia says:
One of the first pornographic films to feature a plot, character development, and relatively high production values, Deep Throat earned mainstream attention and launched the “porno chic” trend…
The film’s popularity helped launch a brief period of upper-middle class interest in explicit pornography referred to by Ralph Blumenthal of The New York Times as “porno chic”. Several mainstream celebrities admitted to having seen Deep Throat, including Martin Scorsese, Brian De Palma,[10] Truman Capote, Jack Nicholson, Johnny Carson,[4] Spiro Agnew, Frank Sinatra, Philip Dresmann and Louis Derfert.[9] Barbara Walters mentions having seen the film in her autobiography, Audition: A Memoir.[11] Jimmy McMillan considers it to be his favorite film.[12]
Cecil’s 1993 article on snuff films seems relevant. Even then, there existed:
News footage and the like in which a death is filmed by happenstance. One commonly cited example is the Zapruder film of the Kennedy assassination. One underground video series, Faces of Death, depicts numerous grisly deaths, some of it apparently drawn from newsreel outtakes, with a lot of reenactments thrown in.
So I’d say that footage with murder is commonly available in the US.
The Faces of Death movie was swiped by some teenager I knew. From her parents or brother, maybe.
She brought it to a sleepover. It was terrible grainy copy.
I mostly remember the people eating what were said to be monkey eyeballs. Grossed me out.
I was more afraid of the Nostradamus film, can’t remember the name but Orson Welles narration was spooky.
I’m like most people, any murder or child rape depiction would turn into evidence pretty quick if it was deemed a true account.
Anything shown in a theatre would be some kinda, so called acting.
I find things all the time on movies that are off-putting. I really hate torture in films. I will get outta there quick if I see it happening.
There is a certain film containing gritty realism which has never got passed the UK censors (BBFC) just yet.
(Please try to not link to paywalled articles.)
In any case, you have brought up examples of commercially-released films that are “controversial” as to content and where the possible objections were addressed and discussed and each jurisdiction passed judgement according to their respective standards, but not true examples of the Thread Title (absent actual proof of Ms Lovelace’s more extreme later allegations).
In the case of The Bunny Game, being so far undisputedly a staged performance, the Thread Title would not apply. If the UK board of standards found against it based on graphic content, that’s because that’s what UK rules and standards are and for some things portrayal itself can be ruled against even if staged. So yes there is censorship in the UK… that was not the question you asked, so “what would happen there (in Denmark)?” In the case of a real film-of-crimes, is still unaddressed.
I don’t know if “staged” is the right word for that film. “Consensual” maybe? It seems the actress was actually branded & beaten on camera, so it’s not fake, but if she agreed to it ahead of time it’s not a crime either.
One scene that has belatedly become controversial was the anal sex scene in Last Tango in Paris.
The scene shows Paul (Marlon Brando) telling Jeanne (Maria Schneider) to get some butter. Paul then holds Jeanne down and pulls her pants off. He uses the butter to lubricate her anus and then forces anal sex on her. Jeanne is crying and telling him no throughout the scene.
The reason that scene is now controversial is the belated public revelation that Brando and the movie’s director Bernardo Bertolucci came up with the idea between them but didn’t tell Schneider what was going to happen. Their reasoning was they wanted her reaction to be genuine. So when Schneider is crying and saying no, she’s not acting out a scene that she had agreed to.
Brando and Bertolucci apparently defended their actions by claiming that there was no actual sex in the scene. But the application of the butter was real and that would legally qualify as sexual assault.
There is a parody of the Tango anal scene in which the guy can’t get it up because the woman brought margarine instead of butter.
I do often use “staged” for performances such such as this where the danger is real but willingly entered and planned as to where does it lead. But I understand your point.
Here is a gift link, good for 30 days, to the same article.