Tory leader David Cameron has called for tougher sentences for rapists, saying too many men "think they can get away with it".
England and Wales have the lowest conviction rate - 5.7% - among leading European countries, he said.
He pledged longer-term funding for rape crisis centres, to change attitudes towards rape through sex education and announced a Tory review of sentencing.
The government says it has taken action to improve conviction rates.
In a speech at the Conservative Women's Organisation conference, Mr Cameron said: "Studies have shown that as many as one in two young men believe there are some circumstances when it's okay to force a woman to have sex.
"To my mind, this is an example of moral collapse."
He called for "widespread cultural change" and warned that society has become increasingly "sexualised" over the past decade, during which time treating women as sex objects has become viewed as "cool".
He also called for compulsory sex education in schools to drive home the message that sex without consent is a criminal offence.
The Tory leader said some statistics suggested one in 20 women had been raped, yet three-quarters of them never report the crime.
And of those that are reported, just 5.7% result in a conviction, he said.
Average sentences over the last three years for which the information is available have fallen, to less than seven years, he said.
Mr Cameron also said the number of rape crisis support centres had fallen from 68 in 1984 to 45, and funding decisions on those that remained were short-term and being made mid-way through the financial year.
"As a result, these centres are forced to survive hand-to-mouth and often face the threat of imminent closure," he said.
"All this has led to an appalling and tragic lack of support for the victims of rape."
He said a Conservative government would ensure three-year funding cycles for the centres to give them "certainty and stability".
Mr Cameron said that people must never forget "harrowing" stories, like that of 17-year-old Lindsay Armstrong, who was raped in a park in New Cumnock, Ayrshire, in 2001.
She killed herself less than two weeks after her attacker was found guilty, after undergoing a "brutal cross-examination" in court, he said.
Mr Cameron said people should never forget Miss Armstrong's story
The Tory leader said: "By keeping the memory of Lindsay Armstrong alive - as her parents do through their support group - we can make sure no one forgets the need to end sexual violence against women."
In eight out of 10 rape cases, victim and suspect are known to each other.
But juries tend to be more likely to convict in so-called "stranger rape" cases where there is often semen, blood or saliva from the suspect at the crime scene, injuries on the victim and CCTV or eye-witness evidence.
Asked about the conviction rate, Home Secretary Jacqui Smith said: "It isn't good enough, which is why we have said that in every single police force area there needs to be a plan for improving the conviction rate from every stage - from the point where a woman reports it through to gathering the evidence and supporting them through court."
But she said the Conservatives had "opposed some of the things that we've tried to do in the last 10 years".
Ms Smith added: "They opposed tougher sentences in 2003 for serious sexual offenders. They opposed the retention of DNA, which actually just in the last three years has convicted 90 rapists."
Katherine Rake, director of the Fawcett Society campaign group, said the rape conviction rate was "a national disgrace" and crisis centres were at risk of closure because of a lack of funding.
She said she hoped the comments would be the start of a serious debate on the issue and help to give it the "political priority it deserves".
Alan Gordon, vice-chairman of the Police Federation of England and Wales, said forces had "invested a considerable amount in training and are now investing in rape investigation suites so that people will feel comfortable about coming forward and talking to the police."
Mr Cameron announced that shadow justice secretary Nick Herbert will carry out a review of rape punishments to ensure they are "proportionate to the crime".