That conflict has been operating at "cold war" status since the end of the Second Vatican Council that concluded in 1965.
The church's liberal wing expected the council's relatively modest theological and liturgical reforms to lead Catholicism toward something like the path mainstream Protestantism took during that era: married priests, female priests, a reversal of the church's prohibitions on homosexuality, divorce and contraception.
The traditionalists rejected that path and somewhat surprisingly managed to steer the church away from it, at least until the election of Francis as pope in 2013. But neither side has yet managed a decisive victory.
This isn't the first time that clerical-abuse scandals have become a proxy battle in that doctrinal war.
They are frequently invoked by both modernisers and traditionalists as evidence to support their views: the modernisers for an end to the male, celibate priesthood, and the traditionalists for the dangers of tolerating homosexuality, even tacitly, given that most of the abuse involved pubescent or post-pubescent boys.
The best evidence we have to assess either set of claims comes from a report done by criminologists at John Jay College of Criminal Justice in 2011.
What that evidence suggests is that both sides are wrong.
The timing of the abuse, which rose in the 1960s and started to decline in the 1980s, doesn't support causation by ancient prohibitions on married or female clergy.
But the timing also can't be explained by what seems to have been a late-1970s influx of gay-identified seminarians.
Both explanations nonetheless retain a certain intuitive appeal for those who have not read the report, or have done so with a dogmatic rather than disinterested eye.
Vigano himself has faced accusations — which he denies — that as the Vatican's ambassador to the United States he blocked an investigation into possible sexual misconduct by a more-conservative archbishop, John Nienstedt, of St. Paul and Minneapolis.
And his letter's indictments of homosexuality make it clear that he views this as a salvo against the church's liberal wing. All of these factors have been evinced by Francis's supporters as reason to ignore Vigano's claims. Certainly, the claims should be weighed in that light. But dismiss them? Journalists know that this is what whistleblowers often look like: compromised, agenda-laden, grievance-obsessed.
Sources who go on the record with reporters almost invariably have some sort of agenda, if only to see their names in print. If tips and evidence came only from the serenely disinterested, the news would consist of recipes, the weather and photos of kittens.
But reporters then seek to confirm biased information by checking it with other sources, something Vigano has made easy to do by providing a wealth of names and detail.
Right now there isn't much to go on, but the little information available does tend to support at least some of Vigano's claims.
Journalists also ask the accused for comment — comment that Francis has so far refused to provide. None of this is troubling enough to merit papal resignation, but it does demand further inquiry.
Unfortunately, it's hard to pursue that inquiry when the wider war monopolises our attention.
The church can attack the issue of corruption in the hierarchy without settling its intractable disputes over sexual liberalism.
But to do that, it will need to form at least brief alliances across the old battle lines and act as one church.
And for such an alliance to work, everyone will need to decide their common interest in vanquishing abusive clergy outweighs their common fears about losing the wider war.
