Matters that are political are not in themselves matters of faith or morals (although they may be morally relevant), and thus such teachings are not themselves infallible.
I think it’s best if we focus the discussion on the matter of Church authority. It seems that we are not talking about merely “political matters”. We are talking about the duty of societies to God and the Catholic Faith. The teaching of the Church is that societies, no less than individuals, are bound to give God and the True Faith rightful place. And because all rightly ordered societies have a system of government, those rightly ordered governments too are bound to give God and the True Faith rightful place. As, for example, Pope Leo XIII writes:
Nature herself proclaims the necessity of the State providing means and opportunities whereby the community may be enabled to live properly, that is to say, according to the laws of God. For, since God is the source of all goodness and justice, it is absolutely ridiculous that the State should pay no attention to these laws or render them abortive by contrary enactments. Besides, those who are in authority owe it to the commonwealth not only to provide for its external well-being and the conveniences of life, but still more to consult the welfare of men’s souls in the wisdom of their legislation.
As Ehler and Morrall nicely summarize, the Popes repeatedly uphold the idea of, “public acknowledgment of religion by the State
as a logical deduction from acceptance of the premise that God is the Author of civil authority” (my emphasis). Those things which logically derive from matters of faith are themselves within the competence of the Church’s teaching on faith. And therefore, I would argue, the proper relation of the State to the Catholic Faith is not mere politics but falls squarely within the sphere of faith and morals.
You tried the make the absolute distinction between societies and governments, but the important point is that the teaching of the Popes does not seem to allow such an absolute distinction. For your position to be valid, it would seem that you would have to 1) prove that the Popes did not make the logical connection described above or 2) prove that they did make the logical connection, but erred in doing so. I think the burden is on you in this matter.
Beyond this, simply stating that a given teaching isn’t formally infallible and proceeding to ignore that teaching is not sufficient. A faithful Catholic is bound to more than that:
This religious submission of mind and will must be shown in a special way to the authentic magisterium of the Roman Pontiff, even when he is not speaking ex cathedra; that is, it must be shown in such a way that his supreme magisterium is acknowledged with reverence, the judgments made by him are sincerely adhered to, according to his manifest mind and will (
Lumen Gentium 25).
To me your view is not in line with LG 25 with respect to the solemn pronouncements of the Roman Pontiffs on the separation of Church and State. It also seems to me that you skirted too lightly over the condemnation of Pope Pius XI of a “social modernism” that simply dismisses the solemn teaching of the Pontiffs on these matters. Again, he condemns those who, “speak, write, and, what is more, act as if it were not necessary any longer to follow, or that they did not remain still in full force, the teachings and solemn pronouncements which may be found in so many documents of the Holy See, and particularly in those written by Leo XIII, Pius X, and Benedict XV.” I do not detect any difference between your view and that condemned by Pope Pius XI. I see you putting forth the view here that it is not necessary any longer to follow the teachings and solemn pronouncements of those Pontiffs on the separation of Church and State. Could you explain again how your view expressed here is not accurately described by Pius XI?
On practical matters, you deploy examples of abuses of government power, but of course
Abusus non tollit usum.. Similarly, you see it as daunting to put the genie back in the bottle with respect to things like rampant pornography and contraception. But pagan societies have been transformed by the Gospel, have then had Catholic governments which did not allow, for example, the distribution of pornography and contraceptives, and this did not disrupt their peace but rather enhanced it. More importantly, these laws had in mind the spiritual welfare of the citizens and not just their temporal “peace”. And in line with the teaching of the Popes, I would suggest that it was precisely governments acting in accord with Catholic teaching that kept unbridled passions from harming the common good, whereas it has been purely secular governments which have caused and abetted the proliferation of these moral evils through complete lack of restraint.
These are important secondary matters. But, as I said, I would really like to focus on matters of Church authority first and foremost in our discussion. Thanks.