Statue of Our Lord surrounded by St. John the Evangelist, St. John the Baptist and Doctors of the Church, at the Basilica of St. John Lateran in Rome.
(Marie-Lan Nguyen, CC BY-2.5, via Wikimedia Commons)
Heterodoxy is never a good thing, because falsehood isn’t, and we know where it ultimately comes from. Orthodoxy is not a matter of mere subjective taste and preference for vanilla ice cream over chocolate, but of objective doctrine.
There is latitude and leeway on some doctrines, such as predestination, or, say, the charismatic movement (which I have defended). But most Catholic doctrines are pretty firmly established by now. So one might ask, “how do we know what is orthodox?” It's easy:
1) Catechism of the Catholic Church
2) Heinrich Denzinger, Enchiridion Symbolorum: A Compendium of Creeds, Definitions, and Declarations of the Catholic Church
3) Ludwig Ott, Fundamentals of Catholic Dogma (revised and updated 2018 edition)
4) Ecumenical Councils [see a multi-lingual resource containing all the conciliar documents]
5) Papal encyclicals
[#1-5 are basically how we determine magisterial Catholic teaching]
6) Good (orthodox!) apologetics and historical materials explaining same if necessary.
If anyone leads people astray by claiming that Catholicism teaches or sanctions doctrine or moral view x, and in fact it does not, God will hold them accountable. Teaching in the Church in any capacity is a very serious business, and James 3:1 (RSV) states: “Let not many of you become teachers, my brethren, for you know that we who teach shall be judged with greater strictness.”
The great apologist G. K. Chesterton wrote eloquently (in his 1908 book, Orthodoxy: written 14 years before he was received into the Catholic Church) about how orthodoxy — far from being a restrictive or negative thing — was wonderfully adventurous and a necessity:
People have fallen into a foolish habit of speaking of orthodoxy as something heavy, humdrum, and safe. There never was anything so perilous or so exciting as orthodoxy. It was sanity: and to be sane is more dramatic than to be mad. It was the equilibrium of a man behind madly rushing horses, seeming to stoop this way and to sway that, yet in every attitude having the grace of statuary and the accuracy of arithmetic. The Church in its early days went fierce and fast with any warhorse; yet it is utterly unhistoric to say that she merely went mad along one idea, like a vulgar fanaticism. She swerved to left and right, so exactly as to avoid enormous obstacles. She left on one hand the huge bulk of Arianism, buttressed by all the worldly powers to make Christianity too worldly. The next instant she was swerving to avoid an orientalism, which would have made it too unworldly. The orthodox Church never took the tame course or accepted the conventions; the orthodox Church was never respectable. It would have been easier to have accepted the earthly power of the Arians. It would have been easy, in the Calvinistic seventeenth century, to fall into the bottomless pit of predestination. It is easy to be a madman: it is easy to be a heretic. It is always easy to let the age have its head; the difficult thing is to keep one's own. It is always easy to be a modernist; as it is easy to be a snob. To have fallen into any of those open traps of error and exaggeration which fashion after fashion and sect after sect set along the historic path of Christendom--that would indeed have been simple. It is always simple to fall; there are an infinity of angles at which one falls, only one at which one stands. To have fallen into any one of the fads from Gnosticism to Christian Science would indeed have been obvious and tame. But to have avoided them all has been one whirling adventure; and in my vision the heavenly chariot flies thundering through the ages, the dull heresies sprawling and prostrate, the wild truth reeling but erect. (ending of section VI: "The Paradoxes of Christianity")
Chesterton offers a delightful word-picture of Catholic tradition (my very favorite description of tradition) in the same book:
Catholic doctrine and discipline may be walls; but they are the walls of a playground. Christianity is the only frame which has preserved the pleasure of Paganism. We might fancy some children playing on the flat grassy top of some tall island in the sea. So long as there was a wall round the cliff's edge they could fling themselves into every frantic game and make the place the noisiest of nurseries. But the walls were knocked down, leaving the naked peril of the precipice. They did not fall over; but when their friends returned to them they were all huddled in terror in the centre of the island; and their song had ceased. (from section IX: "Authority and the Adventurer")
Conversely, Blessed John Henry Cardinal Newman (to be canonized as a saint in the near-future), excoriated the opposite of orthodoxy: the logical reduction of theological liberalism or heterodoxy:
Liberalism in religion is the doctrine that there is no positive truth in religion, but that one creed is as good as another, and this is the teaching which is gaining substance and force daily. It is inconsistent with any recognition of any religion, as true. It teaches that all are to be tolerated, for all are matters of opinion. Revealed religion is not a truth, but a sentiment and a taste; not an objective fact, not miraculous; and it is the right of each individual to make it say just what strikes his fancy. Devotion is not necessarily founded on faith. (“Biglietto Speech” upon becoming a Cardinal, 12 May 1879)
This is no small matter. To be a Catholic is to accept, obediently in faith, all that the Church infallibly teaches, as the Guardian of the apostolic deposit.
We can always grow in our understanding, and better comprehend why we believe what we believe. We must adjust our theological beliefs to be in line with those of the Catholic Church (yes, even given all the scandalous faults of flawed individuals within her domain), rather than vice versa.