For the historian, trained in the rigorous interpretation of evidence, this presents a serious challenge. So much of what passes for an assessment of sectarianism is founded on assumption, belief, preconception, anecdotal and unrepresentative data and even an unwillingness to draw on such credible academic studies as exist.
Typical of the ambiguity and vagueness around the issue was the failure of the Justice Committee of the Scottish Parliament to even try to define sectarianism when debating the still highly controversial Football Offences and Threatening Communications Bill.
The recent report of the Government's Advisory Committee on Sectarianism did little better. Not only did it fail to produce any significant fresh evidence; it also replaced the traditional and satisfactory definition of the problem (a widespread and shared culture of treating individuals improperly because of their religious beliefs) by a new and barely comprehensible piece of social science jargon.
This means assessing the nature and scale of the problem by agreed criteria over time becomes virtually impossible. The issues are complex and the evidence scarce. But one such source (analysis of reported hate crime in Scotland) can provide some conclusions.
Most crucially, this reveals that sectarian aggravated criminal charges in 2012-13 were of relatively minor significance, at 11.7% of the total compared, for example, with racial charges at nearly 70%. Indeed, there were marginally more charges for sexual orientation-aggravated offences than for those on the basis of religion hatred. Moreover, as regards the latter, they usually involved abusive language to police or other public officials; there was little evidence of violence; it usually involved young, frequently drunk young men mainly in Glasgow and the west of Scotland; and in the vast majority of cases, the religious identities of "victims" were not known to perpetrators.
As the sociologist, Michael Rosie, of Edinburgh University, has put it: "The figures reveal a dismal picture of urban incivility, particularly among young men who drink too much." Even more remarkable, given the obsession of government and the media with sectarianism as a social evil, there were fewer than 900 reported charges for religious aggravation in 2011-12 in contrast to nearly 60,000 incidents of domestic abuse reported to police in that year.
These figures do indeed reveal the scourge of what is really "Scotland's Shame", but one that remains unreported and marginalised compared to newsworthy but essentially limited instances of sectarian-based criminality. The focus of academic investigation needs to change from the nature and extent of sectarianism to the fascinating question of the rise of anti-sectarianism.
For most of last century when the disease was rampant and noxious it was little discussed or debated in public. Like an unpleasant smell at a middle-class dinner party, everyone knew it existed there but nobody wanted to talk about it.
Today, with the old monster in its death throes, sectarianism has spawned a new growth sector: a well-financed anti-sectarian industry. A delicious irony indeed.
An abridged version of the Margaret Harris Memorial Lecture in Religion delivered by Professor Devine at Dundee University.