The Human Tissue Act came into force on Friday and it is to be hoped that it will go some way towards clarifying the legal position of surgeons with patients waiting for organ transplants, and, perhaps even more important, of pathologists wanting to carry out research using human tissue.

Until now, if an adult placed his name on the Organ Donor Register, his wishes, when he died, could be overridden by his relatives. This has always seemed to me not only absurd but also insulting to the person who had declared his intentions quite clearly. Why should someone else's scruples count for more than the wishes of a competent person, with his own views about what is for the common good? His wishes ought to have absolute priority. There can be no evidence that a young man who had put his name on the register and who was killed in a car crash had changed his mind about donating organs before he died.

The new law does not go as far as granting absolute priority. Transplant surgeons are still obliged to consult relatives before using the promised organs, but they have to decide for themselves whether the objections raised by the relatives are serious and so strongly felt that the transplant should not go ahead. It is therefore doubtful whether things will change very much. For any objection to the use of the organs of someone recently dead must be based on either irrational sentiment or irrational dogma, or both; and in the nature of the case, the arguments of the surgeon may well not prevail, even if he has to go through them carefully with the relatives.

After the scandal of Alder Hey children's hospital in Liverpool, and the Bristol Royal infirmary - where the organs of children who died were retained without the knowledge of their parents - permission to retain organs or tissue became hard to obtain. Important research using human tissue was seriously threatened. Plainly the doctors involved had behaved carelessly, even insanely, in cases where the organs were stored and not used. All the same, the violence of the reactions was surprising. What did those furious parents believe about their dead children? Did they think that in some way the future of the child had been compromised by the removal of the organs? If I had been such a parent I would have been angry at not being consulted. I can imagine raging against the arrogance of those doctors who seemed to believe that the child's body was their own property, and who thought of the dead child as so much research material. But though such anger is intelligible, is it rational?

In considering the reaction, there seems to be a confusion between two different ideas. The first is that it is right to treat the death of any human being as an occasion for the formal expression of grief and respect, the public recognition of loss - and perhaps irreparable trauma, if the death of a child is involved. This is why the thought of simply throwing away the body of a dead human being is intolerable and offensive. The second is the idea that the person who has died is somehow still living and must be kept intact in death. Yet anyone who does not believe in the literal doctrine of the resurrection of the physiological body (and that is nearly everyone, even professed Christians) must recognise that, after death, the body of their child will disintegrate, whether slowly in the earth or swiftly in the fire of cremation. How can those who object to the removal of organs from their child on the grounds that, as one enraged parent put it, "she cannot love us without a heart" also accept, as a social phenomenon, the increasingly common practice of cremation?

Cremation is still not a universally accepted way of disposing of the dead; but it is widely practised, and even encouraged, as graveyards become full. It is certainly recognised by the church. It would be far better to embrace the idea that, in death, a human being might indirectly benefit others by the postmortem use of organs or tissue than to encourage and foster the superstition that a body must be buried intact, and that otherwise the person has not been properly respected and mourned. The new law is a very modest step in the right direction, but its immediate impact may, sadly, be small.

· Mary Warnock is an independent peer and the author of An Intelligent Person's Guide to Ethics comment@theguardian.com