If religious education is transformed into a form of sociology, why do we need to bother with the specific subject?" asks Glasgow University's Professor James Conroy in his summary of the most ambitious research project ever undertaken on RE. Too often, RE becomes a "cabinet of curiosities", viewed from afar as if on a plodding museum tour, he says. There is no sense of how it feels to have faith, and religions' definitive claims are sidestepped. "Sociology" could read "citizenship", "modern studies" or "history". If RE loses its distinctiveness, it becomes like the study of Marxism or urbanisation - something that should slot into other subjects.
Principal teacher at Paisley's Gleniffer High, David Jack, says RE is unique in the curriculum. "We say to kids that RE is the subject which takes human thinking as far as it goes. That's why the brain starts to nip when you wonder what went on at the start of the universe - no other subject makes that demand."
Citizenship may share aims of respect and tolerance, "but there is a danger that can be in a vacuum," says Heidi Jamieson, an RMPS teacher at Banchory Academy in Aberdeenshire. Her subject shows "where we get our sense of morality from".
"There is a real danger that people equate declining church attendance with declining religiosity or spirituality," she says. "We may be a more secular, consumer society, but people are still seeking meaning."
Joe Walker, principal teacher in an east of Scotland school, argues that his subject makes sense of issues such as the phone-tapping scandals and MPs' convictions for lying.
"You can reduce these to how human beings treat other human beings, the type of stuff we deal with every day," he says. "Children have access to the whole world in the palms of their hands - they really need to understand ways of life and cultures, starting with their own. We do this in a very explicit way."
"It's very important that RME is an exploration," agrees HMIE's Patricia Watson. "It's not just learning about religion, but learning from religion. It's not only about the five pillars of Islam or a synagogue's design features, but also developing you as a person."
RE topics may overlap with work of other departments, acknowledges Ewan Aitken, secretary of the Church of Scotland's church and society council, but it also develops critical thinking. "It's that meaningfulness that makes RME distinct."
He believes RME brings to life Curriculum for Excellence's "four capacities" better than anything else, allowing pupils to say: "This feels different to other subjects - I'm asked to think for myself, ask questions, come to conclusions, then defend them."
Some teachers, however, fear CfE's cross-curricular emphasis will sideline their subject, and Professor Conroy dismisses optimism around the reform as "incredibly naive", predicting that policy-makers' antipathy to RE in England will spread north.
Clare Marsh, the Humanist Society of Scotland's education officer and retired biology teacher, perceives what "could be a great subject in the right hands", but remains a tool for imposing religious belief in a significant number of schools. This view is rejected by most.
"Any claim that anybody makes about teachers pushing a religious view, it just couldn't be further from the truth - RME teachers are in the business of getting pupils to think," says Hilary Scott-Heaney, teacher at Glasgow's Cleveden Secondary and chair of the Association for the Teaching of Religious Education in Scotland.
RE is the only subject with separate Curriculum for Excellence outcomes for denominational schools, reflecting Catholic Church advice that teachers propose its beliefs as objectively true. But Michael McGrath, director of the Scottish Catholic Education Service, insists there is room for sceptical discussion.
"It's about a mature, individual response - not indoctrination," he says. "The priority is to get pupils to the stage where they can make their own decisions and responses to God."
Although the findings in Does Religious Education Work? - which looked in detail at only two Scottish Catholic schools - are presented as largely applicable in all sectors, teachers in Catholic schools emerge as more sanguine.
Aberdeen University RMPS lecturer Graeme Nixon points to a distinctive legislative feature: the "conscience clause" allowing parents to withdraw children from classes, a legacy of the 1872 Education Act. This, he says, could perpetuate misconceptions that children are force-fed religion.
He argues that citizenship is far more "prescriptive and confessional" in contrast to RE's approach: "We are not forcing kids to be moral."
Today's RE may even make teenagers happier. Philosophers have identified a desire for a meaning to life that becomes acute at secondary age; RE specialists believe their subject alone meets that need.
"The point about catering for existential needs of pupils, whether secular or religious, is powerful," says Mr Nixon. "Schools need to allow pupils to develop, recognise and critique their world view in order to ensure better thinking - but also perhaps a degree of contentment."