The film shows a couple (Ryan Gosling and Michelle Williams) at the start and end of their relationship The director of Blue Valentine has said the recent battle over its certificate in the US has helped open a debate over cinema sex and violence.
The film won an appeal over its adults-only NC-17 rating and was released with an R rating instead.
The marital film drama, which opens in the UK this weekend rated 15, is in the running for two Golden Globe awards.
Ryan Gosling and Michelle Williams are nominated for best actor and actress in a film drama.
US ratings are set by the Motion Picture Association of America (MPAA), which originally awarded the NC-17 rating for a “scene of explicit sexual content”.
“I think the MPAA made a mistake,” director Derek Cianfrance told the BBC this week.
“They were humble and generous to reverse their decision and I have a lot of respect for them for that.
“It’s started a big discussion in America about why is sex taboo and why is violence okay. I think the MPAA has to re-evaluate its stance on things.
“I feel like my kids will see far worse things during commercials on football games – violence and guns. Blue Valentine is just about intimacy and emotion. There’s very little nudity in the film. It’s more about naked emotions.”
Derek Cianfrance (left, with Michelle Williams) conceived the film in 1998 The film’s new R rating means those younger than 17 can see the film if they are accompanied by an adult.
Blue Valentine is the story of the dying relationship between couple Dean and Cindy (played by Gosling and Williams).
It juxtaposes scenes of their courtship, set several years earlier, with painful scenes of marital breakdown in the present.
The filming required Gosling and Williams to undergo hours of demanding sex scenes.
“Michelle and Ryan gave such brave and emotionally naked performances,” said Cianfrance.
“I’m so proud of them. I really admire actors that are willing to be vulnerable and willing to take big risks on the screen. They deserve any accolade that comes their way.”
He added: “We tried to treat the sexuality in Blue Valentine with responsibility. There are consequences to the sex in the film. We treated the sex as we treated every other scene – with a certain kind of honesty and raw integrity.”
The film has been a 12-year journey for Cianfrance. He had re-drafted the script 66 times since 1998. Both Gosling and Williams were attached to the project for several years before it finally started shooting.
“I felt like the movie was cursed, but once it started shooting we were blessed because all these magic moments started happening in front of the camera,” said Cianfrance.
Whatever happens at the Golden Globes, the director is keeping an open mind about its Oscar chances.
“Those things are so out of my hands. For the last year I’ve been on the road supporting the movie. There’s nothing else Michelle and Ryan can do.
“The business and the critical acclaim has been amazing and it’s heartening to know that something that was so personal to me is now becoming personal to other people.”
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