IN her column last week, Mary Holland described abortion as "the issue that will not go away". She is right. The subject is being debated, not just in Ireland, but throughout the contemporary world.

Why should this be? Why should people of such different cultural and religious backgrounds be so exercised by this question?

The answer is that the right to life of unborn children touches on several wider issues. Is everyone to be considered a human being or should we exclude certain groups, such as those without cognitive capacity (PVS patients), the seriously mentally ill, the unborn and "defective neonates"?

Even if we do not go so far as denying human status to them, should we regard their life as less, than fully valuable and worthy of protection? Would they be better off dead than alive? Should there be an entitlement to terminate their lives directly? Should there be an obligation to do so in some cases?

These common themes arise, of course, in relation to abortion, but what is striking about them is that they range so widely, extending to the recently born, the physically and mentally ill, and the aged.

Some common answers also emerge. Naturally, the emphasis varies, but two opposing positions can be discerned.

On one view, the value of a human life is determined by its particular quality. The capacity to make decisions, to enjoy life's experience and to relate to others gives to an individual's life a richness of quality, and thus value, vastly in excess of the quality and value of the life of one who is incapacitated through illness or old age or who lacks autonomy through lack of age.

On the other view, everyone's right to life is considered to be of equal value. The ill, the unborn an the aged have no less right to legal protection than anyone else. This approach translates into a legal protection of the unborn from abortion.

HISTORY reminds us that those who are excluded from society's fits lose their visibility, and their human status becomes harder to see. In non egalitarian societies, the excluded can be so effectively removed from people's vision that they cease to be regarded as an issue.

This process occurs almost inevitably. It results in good people no longer being sensitive to the discrimination that is at the heart of their society; almost invariably, incidentally, supported by the law.

There is no doubt that the international trend to legalise abortion is based on a conscious policy of treating the lives of the unborn as less than fully deserving of protection. Whatever other arguments may be offered in favour of legalised abortion, cherishing all children equally is not one of them.

I believe that most people in Ireland wish to have full legal protection for the unborn. That was clearly their intention when they voted for the Eighth Amendment in 1983 and there are strong indications that it is their intention today. Perhaps, I'm wrong about this. It is always possible that a referendum will turn out surprisingly. But what cannot be denied is that the voters have a democratic, entitlement to determine the matter in a referendum. At local level, there is strong support for a referendum. More than three quarters of the county councils are in favour of this course.

Should we shy away from the subject of abortion because it is divisive? I think not for two reasons. First as a practical matter, there is no way of avoiding the issue. If we do nothing at a constitutional level, legalised abortion, would become a reality. Second, it is the nature of political discourse and of constitutional reform to confront differences relating to issues of principle and of policy.

At a more basic level, the unborn force us to consider what the demands of a humane society are. At the heart of a humane society is an almost instinctive response to dependency, weakness, immaturity and small size.

That instinct is there in young children, who are open to the wonder of life in all its manifestations. The instinct is based not on sentiment but on an awareness of the direct link between dependency and the need for protection. Political and cultural changes can sometimes make us lose sight of that connection. Our politicians have the opportunity to give focus to it by a referendum offering legal protection for the unborn.