As an institution, the Catholic Church sprawled over the Roman Empire and eventually much of the world, but it had a central command and single organizational structure. There was a hierarchy: the Pope, the cardinals (their red vestments led to a certain red bird in the American Midwest being named after them), the archbishops, bishops, monsignors, etc. down to the parish priests. For all of that, you need rules. So the Church established canon law—the oldest body of law still existing. And penalties for disobeying it could be severe.
But canon was about more than bureaucratic rules. The Church was also about religious beliefs, which are in their own terms about ultimate realities: from the nature of God to the meaning of scriptures. The Pope ruled on matters of faith and morals, sometimes with the advice of Church councils, and canon law made his rulings explicit in terms of what you were to do and what you were to believe.
That was the theory, anyway. Eventually the laws declared as canon by councils, bishops and popes grew to enormous proportions, with some laws directly contradicting others. But even so, canon had consequences.
Canon law could be quite detailed, and what might strike outsiders as a minor disagreement could be condemned as heresy, punished at the very least by exile (excommunication: you got thrown out of the Church) but penalties also could include torture and being burned alive at a convention---well, they called them “Councils.”
This suggests a different edge to the many Star Trek canon debates I’ve witnessed over the years at conventions and on various web sites and boards. I was raised Catholic, so I’ve sometimes had the image in my mind of Church scholars debating the number of angels that could dance on the head of a pin. Or was that the number of decks on the Enterprise-A?.. But to be found in error meant your soul was in peril.
So now we have Star Trek canon, as defined by sermons on the Paramount and the Star Trek encyclicals—sorry, Encyclopedia. But while fan feuds over canon can appear overwrought and ridiculous at times, the sense that something important, even essential is at stake, is not really wrong.