Inclusion has become a "misshapen notion" used by ideologues to justify same-sex marriages and abortion, the Archbishop of Glasgow told the annual gathering of Scotland's Catholic secondary heads.
Archbishop Mario Conti said the true and "very positive" meaning of inclusion had become obscured, and that the prevailing orthodoxy did not permit dissenting voices.
As a result, marriage was not a word used exclusively in the "original and traditional meaning"; "parents" were not necessarily the "biological progenitors of children"; registers could be altered to "disguise a change of sex"; and there was "sanctioned killing of unborn children".
Archbishop Conti, speaking at the annual conference of the Catholic Headteachers' Association of Scotland, said everyone had a right to respect, irrespective of their views. However, inclusion had to be founded on objective truth rather than relativism: "If everyone is special, then no one is special."
He deemed it important that young people be trained to discern between "inalienable rights based on natural law itself" - such as education and freedom of worship - and those resulting from "ideological pressure on government".
Catholic schools were upholders of true inclusion, the Archbishop said, despite the argument that denominational education was inherently not inclusive. "It is very easy for the social commentators to pitch the notion of inclusion against the continued provision of separate Catholic schools and suggest that the two cannot co-exist," he said, describing holders of that belief as "short-sighted, even blind".
He added: "I want to challenge that, and I want you to challenge it at every turn. Our Catholic schools are inclusive - they do not turn children away on grounds of race or religion, and there will be scarcely a Catholic school in the country which does not have its fair share of Protestant, Muslim, Hindu or Sikh children, or those whose parents have no faith."
John Reilly, CHAS treasurer and head at Glasgow's St Mungo's Academy, chaired the talk and concurred that "the rock Catholic education has been built on is inclusion".
Michael McGrath, director of the Scottish Catholic Education Service, said: "If Catholic schools are about anything, they are about helping young people to have a sense of moral values."
While all schools were "moral communities", Catholic schools had the advantage of a "whole Catholic school" tradition, through which to articulate these values; other schools struggled to draw on a shared understanding of religious tradition because of their "secular context".
Mr McGrath pointed to the difference between A Curriculum for Excellence religious education outcomes and experiences for Catholic and non- denominational schools, which were "worlds apart". The Catholic guidance was "not merely about helping young people learn about God, religions or faith groups - it's about helping young people respond to God's call to relationship with God, through relationship with others".