Scotland's churches have expressed doubts about government moves to improve rights on adoption for unmarried and same sex couples.
Cardinal Keith O'Brien said the move was "gravely immoral"
The Catholic Church and the Church of Scotland believe such a change may not be in the best interests of children.
Cardinal Keith O'Brien said to allow homosexual couples to adopt was "contrary to the common good".
Morag Milne, convener of the Church of Scotland's church and society council, said the plan raised difficult issues.
Under the new legislation, outlined by the Deputy Education Minister Euan Robson on Friday, same sex couples, as well as unmarried couples, will be able to adopt.
At present, only one member of an unmarried couple can adopt, the other receives separate rights to live in the same house as the child.
But in future, if the partners can prove they are part of an enduring family relationship then they will be allowed on the road to adoption together.
Cardinal O' Brien said the review which had led to the recommendation was in part positive and practical.
However, he added: "The proposals to permit homosexual couples to adopt are contrary to the common good.
"Such a measure would distort the understanding of the family, cause harm to children and promote the status of homosexual relationships.
"Homosexual unions are notoriously fragile and unstable and the small number of homosexual couples living together make the suggestion that this measure would increase the number of potential adoptive parents unrealistic."
'Marriage is best'
Cardinal O'Brien went on to say that the move was "gravely immoral" and contradicted the United Nation's convention on the rights of the child.
However, Calum Irving, director of the gay and lesbian rights group Stonewall Scotland, said the cardinal's comments made it hard to believe that he had the best interests of children at heart.
Mr Irving added that he believed the head of Scotland's Catholics was putting his own "personal prejudice and misunderstanding" before the potential benefit a child would receive from being in a loving stable relationship.
He went on: "I think it is more appropriate that an adoption panel, rather than the Catholic Church, makes an assessment of the stability of a couple's relationship and suitability to raise children."
Ms Milne said the Church of Scotland saw marriage as the best way of providing a happy and stable environment for a child.
She explained: "For a child, welfare is seen in terms of security and happiness and stability and a loving environment.
"The church sees marriage as the best way of providing exactly that situation of stability and security and happiness."
The details of the Scottish Executive plan will now be subject to a public consultation exercise.