Why do Americans have their doubts about executing Karla Faye Tucker by lethal injection at midnight tomorrow? Is it because she had been provoked beyond endurance by the man she killed, who used to park his Harley Davidson in her front room? No. Not even the fact that the motorbike leaked oil, making a terrible mess of the carpet, was grounds for pleading justifiable homicide. Even in America, where McDonald's can be sued for making its coffee hot and therefore dangerous when held between the knees while driving.

Is it, then, that she was such a sad low-life that she never really stood a chance in life? No. She may have been a prostitute by the age of 11, addicted to heroin, and out of her tree on the night of the murder, but this is America, where it is compulsory to believe that everyone has a chance of making it to the top and no excuses are accepted.

Besides, if the damage done by abused and broken childhoods could be entered in clemency, very few of those presently awaiting execution on death row would be there. And the fact that Tucker had taken an astonishingly unlikely combination of drugs on the night she murdered the biker and his girlfriend with a pick axe as they lay in their beds serves only to worsen, not lessen, her crime in the eyes of most Americans.

No, the reason that America hesitates is because Tucker is female. Since the death penalty was reintroduced in 1976 (after a four-year remission, the all-too-brief zenith of American liberalism), 432 human beings have been killed in cold blood by agents of the American people acting in the name of justice. Of these, only one was a woman. As Natasha Walter argues in her book urging the mobilisation of a "New Feminism", statistics prove that women still experience discrimination.

Governor George W Bush Jnr, the son of the last president who would like to be the next, must be hoping that the Texas parole board does not give him the option today of commuting Tucker's sentence to life. He finds himself caught in the cross-currents running through the American electorate between two popular conservative instincts. In Karla Tucker's case, the irresistible force of its fierce support for the death penalty meets the immovable object of the deep structure of American attitudes to women.

Of course, this is not a simple case of sexism, and American feminists, new or old, have not been taking to the streets to demand a pardon for Tucker on the grounds that she was oppressed by a male-dominated society. Although there would be a respectable argument for that, and the symbolic masculinity of that Harley Davidson in her sitting room almost invites academic feminist commentary.

The conservative support for Tucker is not just because she is a woman, although that is a large part of it. The one woman who has been executed in the US since 1976 was Velma Barfield, in North Carolina in 1984, who poisoned four people including her mother. But she was "a tough-looking old broad and nobody paid much attention", according to Newsweek's correspondent. Tucker, a telegenic 38-year-old, has benefited from the sentimental code of chivalry. In the days of "old" feminism, this might have been condemned as part of the ideology of patriarchy: today the point has been made. Being polite to women is one thing; treating them differently has to be justified in each case.

And there is no reason for treating Tucker differently from male murderers, many of whom have suffered worse discrimination on grounds of the colour of their skin than she may have done on grounds of her sex.

But the other reason why conservatives have taken up Karla Tucker's case is because she has converted to fundamentalist Christianity. The religious right's one-time presidential hopeful, Pat Robertson, pleaded with Governor Bush on 60 Minutes, saying that if he "lets this sweet woman of God die, he's a man who shows no mercy".

To which all opponents of the death penalty should respond "Amen"- if not "Hallelujah". If religious right-wingers in America can see the argument for mercy in the case of what seems like genuine remorse and rehabilitation, then perhaps there is hope. Tucker has been a model prisoner, helping fellow inmates with drugs problems, and Mr Robertson says that because she has been born again, God must have forgiven her.

It is too optimistic to hope that this principle might soon be applied more widely. But the fact that opinion polls in Texas are evenly divided over Karla Tucker's fate could be the start of something. Let us hope that more and more Americans will come to realise that, if it is wrong to execute her because she is a God-fearing woman, then it is wrong to execute anybody.