Cult effects culture. A people cannot efficiently coordinate their activities except insofar as they share a common understanding of the way things are, and of the proper way to deal with them. At the very least, they must agree about what is real, what reality is like, what it is for, and so forth; they must agree about First Things, and indeed Most Things. This they generally do, without ever even noticing all their myriad agreements; men rather tend to notice only their irksome disagreements, however petty.
Thus to cohere, a culture must recur to its common cult, and must rehearse it together. So is there always an established religion.
A people among whom heterodoxy regarding First Things begins to gain a foothold begins ipso facto to become confused in their motions: in their heads, hearts, and acts. Their loyalties are then divided, and so vitiated, at least at the margins.
Heterodoxy is cold civil war. Let it compound long enough, and it will go hot. So healthy societies must control for heterodoxy, especially about First Things.
To control for heterodoxy, a society must understand its orthodoxy quite well. So must there be always an established dogma regarding First Things, pervasive inculcation of its doctrines in the young, ritual repetitions of its logic, rehearsals of the sacred texts that encode it, a canon of law to enforce its moral ukases, and in its immunological defense something like the Inquisition. If the Inquisition can’t nip heresy in the bud, it will flourish like a weed, grow powerful, and spread. Things will get more and more out of hand, and harder to control. In the limit, social survival will depend upon costly, dangerous moves such as the Albigensian Crusade or the American Civil War.
This is why foreigners, heretics and innovators are more or less despised: as agents of heterodoxy, they are as it were vectors of memetic disease in the body politic, and their influence must be minimized if a people is to survive. The emotional reaction to the heterodox is radical, and violent: it motivates pogroms, and witch hunts, and persecutions, which can work tremendous damage to the social fabric, sicken and weaken it the way a high fever does a man.
So, there is always an Inquisition. It may be effective, or not; may be violent, or not; but it is always there. When its operations are unnoticed, that is because they are not so much needed – as when an educated immune system destroys an invading virus before symptoms appear.
Men cannot serve two masters. They cannot divide their loyalties, if their lives are to work. They must choose. So then likewise for their societies.
A society that is arguing about First Things, then, is already deeply sick. The virulence of its controversies is an index of its disease. It is bound for some sort of purgative crisis, in which all but one religion will be spewed forth, and destroyed.