A kind of propaganda frequently employed in times of crisis in order to agitate huge masses of people against some alleged common enemy for the stated purpose of defending the foundations of civilized society when, in fact, what's intended to protect is just the status-quo and the continued power or the ruling chaste.
This kind of rhetoric is commonly associated with war propaganda, but it is also widely employed in times of peace in social discourse and "scientific communication", where it is an especially prominent feature of both State Pseudoscience and Pseudo-Liberalism, as a mean to attack dissenters and suppress rational thought.
The Crusade Rhetoric is made up of four features:
1) Invasion Rhetoric: presenting the danger of an "invasion". Our civilization and/or values are being under assault by an horde of dangerous "anti-"this, "anti-"that barbarian invaders.
2) Conceptual Blurring: kind of distinctions and all subtleties are collapsed into a simplistic dichotomy between "us" and "them", where all oppositions are presented as one single amorphous, indistinct mass of subhumanity. In a struggle to defend Christianity there is zero need to differentiate between muslims, heretics, atheists, satanists, etc.; they're infidels, and that's all that matters; similarly, in a struggle to defend "The Science" (keyword for: corporate dogma) there is zero need to differentiate between "anti-vaxxers", Flat-Earthers, conspiracy theorists, "russian bots", etc.; they're, again, infidels, and that's all that matters.
3) Collapse Rhetoric: fearing an imminent fall into chaos and barbarism. It must be constantly stressed how the current dogma are the foundation of all that's good and true, and must be protected at all costs in order to avoid some kind of civilizational collapse (the triuph of the forces of Satan / a return to the Dark Ages).
4) Social Militarization: fomenting a mass mobilitization against the threat, one that has no concern for trampling over people's rights. We're at war, and in a war we can't afford the luxury of being cautious, or caring about rights and freedoms: we need brave soldiers, powerful weapons, Holy inquisitions against heresies, and "task-forces" against "fake-news".