The report from the Free Church of Scotland study panel comes as responses to the Scottish Government’s consultation on gay marriage are being considered.
Referring to same-sex couples, the report said: “By getting the right to marry, they get more respectability for bringing up children (they already have the right to foster and adopt).
“This is a huge social experiment in which the guinea pigs are children. That is not fair or just to children and does not safeguard their rights.
“It is really being pushed in a doctrinaire way by the gay lobby without any consideration of the harm that it will do.”
The church said that civil partnerships already give same-sex couples the same legal rights as marriage, and that there is no need to introduce same-sex marriage.
The Scottish Government launched its public consultation stating it “tends towards the view” that same-sex marriage should be introduced but that faith groups and their celebrants should not be obliged to solemnise the wedding ceremonies.