When people see its consequences, the truism goes, they will be so appalled that public support for change will build up an unstoppable head of steam.
The death of Savita Halappanavar might do just that for the women of Ireland.
Halappanavar, 31, was 17 weeks pregnant with her first, much-wanted baby when she went to Galway's University College Hospital in pain. Doctors told her that her cervix had opened and amniotic fluid was leaking. Her pregnancy was ending and there was no hope for the child.
Over the next three days, in agonising pain, Halappanavar repeatedly begged for an abortion to get the miscarriage over quickly. Could doctors not induce the labour so she could give birth sooner?
That heartbeat stopped after four days and only then was Halappanavar taken to have the contents of her womb removed. She developed septicaemia, or blood poisoning, and was dead three days later.
Obstetrics 101 tells us that sepsis is more likely if the mother's membranes stay ruptured for a long time, or if she retains ''products'' in her womb after miscarriage, termination or delivery. A dilated cervix is like a open wound.
Halappanavar's homeland of India is aghast and there have been diplomatic flurries of concern. Three separate inquiries are under way into the catastrophe and no doubt there will be findings as to whether or not medical negligence was a factor.
That was a straw eagerly clutched by some defenders of the Irish Catholic Church after the scalding rage that erupted over Halappanavar's case.
''It has nothing to do with the church,'' one deeply Catholic woman assured me sharply. ''It sounds like medical negligence. And, anyway, it happened in a state hospital.''
She was channelling Pontius Pilate washing blood from his hands.
In Ireland, politics is deeply intertwined with Catholic doctrine and the institutional power of the church - and the church's tough stance against abortion has protected a near total ban on the procedure.
Ireland still has on its books 1861 legislation that makes it a crime to procure a miscarriage.
A 1983 amendment to the constitution acknowledges the right to life of the unborn child but is also meant to give equal right to the life of the mother.
In 1992, Ireland's Supreme Court was forced to interpret that during the case of X, a suicidal 14-year-old rape victim.
The government was trying to stop her going to Britain to abort the pregnancy that had resulted from the rape.
The court ruled that if there was a substantial risk to the mother's life - her life, but not her health - it would be lawful to terminate.
Irish governments have prevented that judgment from coming into effect by failing to pass laws that would affirm and clarify it.
More than 4000 Irish women each year go to Britain to end pregnancies, according to British health statistics, with almost one in 10 Irish pregnancies ending in British abortion clinics. An unknown number go to other European countries.
''Abortion tourism'', they call it.
Years ago, it could be argued that the influence of church doctrine on the Irish government was democratic - the majority believed in Catholic teachings, so it was fair enough that they were reflected in Irish law and that church leaders were consulted about planned legislation.
But that is no longer the case.
A poll in The Irish Times found that 77 per cent now believe abortion should be permitted in some circumstances.
Other polls have found the hold of the church is weakening more generally - 77 per cent of Irish now think there should be female priests, 90 per cent want married priests and 70 per cent say the church's teachings on sexuality are not relevant to them at all.
That is not discouraging to Cardinal Sean Brady, the head of the Irish church, who announced in August that he would promote a lobbying campaign involving ministers and MPs to oppose any change over abortion.
Australia's cardinal, George Pell, has expressed concern that the furore over child abuse has scapegoated the Catholic Church. The Irish pro-choice movement is not scapegoating the Catholic Church but holding it up to modern accountability.
All the major religions are guilty of some form of systematic abuse of women.
Victims of rape have been executed in the name of Islam; Hinduism abandons widows to homelessness; Orthodox Jews in Israel spit on women they deem immodest and try to force women to sit down the back of buses.
The fact that a religion invokes God, claims to be a path to transcendence and offers society many benefits does not exempt it from outside scrutiny of beliefs that cause harm.
Catholic Ireland's judge is likely to be the European Court of Human Rights, which criticised the government two years ago for not having clarified the Supreme Court ruling.
The Irish government then set up an expert panel to report to its health minister and the government has said it will respond at the end of this month.
This will be a moment of truth for the Republic of Ireland.
Many old-time Irish republicans believed the country couldn't come of age until it was united, with Ulster returning to the national fold.
But perhaps a more important coming of age involves Ireland standing tall as a secular state where civil law can differ from, and override, canon law.
One person's religious freedom must end where it hurts another's right to health or happiness - or, as in Halappanavar's case, the right to life itself.
As protesters outside the Irish Parliament last week pointed out, Halappanavar had a heartbeat, too.