Three excerpts of doctrinal writings on political pluralism. The first is a synthesis of the doctrine. The second is a more detailed analysis. The third is a relatively unknown article of St. Josemaria published in a newspaper.
Pluralism in the social sphere among Catholics
The same good objectives can be achieved by different pathways; it is reasonable, therefore, that there be a pluralism of opinions on how to achieve a specific social goal. It is natural that the backers of each solution legitimately seek to carry it out. Nevertheless, no option has the guarantee of being the only appropriate alternative (among other reasons because politics to a great extent is concerned with future events, and thus is the art of the possible), and even less so, of being the only one that accords with the Church’s teaching.  “No one is allowed in the aforementioned situations to appropriate the Church’s authority for his opinion.” 
Therefore all the faithful, particularly the laity, have the right that their legitimate autonomy be recognized in the Church to take part in temporal affairs in accord with their own convictions and preferences, as long as these are in agreement with Catholic teaching. And they have the duty not to implicate the Church in their own decisions and social activity, never presenting their solutions as “Catholic” solutions. 
Pluralism, while a positive good, should never be confused with ethical relativism.  Pluralism is morally admissible when the goal is a true personal or social good; but not if the decision is contrary to the natural law, to public order, and to the fundamental rights of the human person (cf. Catechism of the Social Doctrine of the Church , 1901). But outside these extreme cases, pluralism should be fostered in temporal matters, as a good for personal, social, and ecclesial life.
 Cf. Vatican Council II, Const. Gaudium et spes , 75; Paul VI, Apost. Letter, Octogesima adveniens , 50; Compendium of the Social Doctrine of the Church , 417.
 Ibid ., 43.
 Cf. St. Josemaría, Conversations , 117
 “Such relativism, of course, has nothing to do with the legitimate freedom of Catholic citizens to choose among the various political opinions that are compatible with faith and the natural moral law, and to select, according to their own criteria, what best corresponds to the needs of the common good. Political freedom is not—and cannot be—based upon the relativistic idea that all conceptions of the human person’s good have the same value and truth, but rather, on the fact that politics are concerned with very concrete realizations of the true human and social good in given historical, geographic, economic, technological and cultural contexts. From the specificity of the task at hand and the variety of circumstances, a plurality of morally acceptable policies and solutions arises” ( Doctrinal Note on Some Questions Regarding the Participation of Catholics in Political Life , November 24, 2002, 3). Cf. Compendium of the Social Doctrine of the Church , 569 and 572.
Avoiding an ambiguous pluralism
By Angel Rodríguez Luño in EWTN in Connection Between the Political and Religious Spheres
On this practical level a legitimate political pluralism of Catholic citizens exists. Christian conscience is bound to certain fundamental values, but often different policies for their realization are conceivable and different opinions can exist on the interpretation of the foundational principles of the political theory which is best adjusted to the specific needs and character of a people, or the technical complexity of certain political problems can leave room for different morally acceptable solutions.
It is the Church's right and duty to pronounce moral judgments on temporal situations which are required by faith or morality, but it is beyond its mission to specify and suggest concrete proposals, or even less, uniquely binding proposals for problems which admit different solutions according to Christian conscience (cf. Note, n. 3).
To propose and choose options considered most suitable for the common good is the task and responsibility of all who can legitimately engage in politics: believing and non-believing citizens, parties, institutions, governing bodies.
It is a very different thing for a Catholic — and, by another right, also for any citizen — to confuse the plurality of politically legitimate options "with an ambiguous pluralism in the choice of moral principles or essential values. The legitimate plurality of temporal options is at the origin of the commitment of Catholics to politics and relates directly to Christian moral and social teaching. It is in light of this teaching that lay Catholics must assess their participation in political life to be sure it is marked by a coherent responsibility for temporal reality" (Note, n. 3).
Political pluralism is by no means similar to ethical relativism or pluralism, according to which every conception of man's good is as valid as any other (cf. Note, nn. 2-3). Nor can that which is openly opposed to the essential needs of the common good be legitimately appealed to with regard to political strategies or policies (abortion, destruction of human embryos, etc.) (cf. Note, n. 4).
In the face of the conformity and relativism which are spreading in many political environments, and which at times assume connotations of intolerance or injustice, the Doctrinal Note on Some Questions Regarding the Participation of Catholics in Political Life intends above all to remind Catholic citizens of a social and political commitment which is consistent with the Christian conscience.
Vatican Council II cautions that "one of the gravest errors of our time is the dichotomy between the faith which many profess and the practice of their daily lives" (Gaudium et Spes, n. 43).
The correct understanding of laicity and pluralism is nevertheless necessary in order to better frame, in the context of current democratic societies, the urgent need for commitment, so that public life be ordered according to the values of freedom, justice, peace, solidarity, etc., which are inseparable from Christian conscience.
No dogmas in temporal matters
By St. Josemaria in Riches of the Faith
There are no dogmas in temporal matters. It is contrary to human dignity to try and lay down absolute truths in things that are necessary matters of opinion, on which people will have different viewpoints depending on their interests, cultural preferences and personal experience. Trying to impose dogmas in temporal affairs leads one inevitably to do violence to other people’s consciences, to fail to respect one’s neighbor.
I don’t for a moment want to suggest that Christians should be indifferent or apathetic about temporal matters. But I do think that Christians have to combine their passion for civic and social progress with an awareness that their own opinions are limited, and hence they have to respect other people’s opinions and love legitimate pluralism. Someone who cannot do this has not understood the message of Christianity in all its depth. It’s not easy to understand it fully and in a sense, we never will, because our tendency to selfishness and pride never leave us. This means we are all obliged to examine our conduct constantly, comparing our actions with Christ’s, to recognize that we are sinners and begin over again. It’s not easy, but we need to do our best.
When God created us he ran the risk and adventure of our freedom. He wanted history to be real, made of genuine decisions, not a fiction or a game. Each individual has to experience his or her personal autonomy, with the hazard, experimentation and uncertainty that it involves. Let’s not forget that although God has given us the security of our faith, he hasn’t revealed to us the meaning of all human events. Together with things that Christians find clear and certain, there are very many others which are open to opinion, i.e. a certain degree of knowledge of what may be true or right, with no absolute certainty. In such cases, it’s possible that I’m mistaken, but even if I am right, other people may be right too. An object that looks concave to me looks convex to people seeing it from a different standpoint.
An awareness of the limitations of human judgments leads us to recognize freedom as a necessarily condition for living in harmony with others. But it isn’t everything, and it isn’t even the most important thing. Respect for freedom is rooted in love. If other people think differently from me, is that any reason for us to be enemies? The only reason for that would be selfishness, or the narrow-mindedness of thinking that there are no values other than politics and business. But Christians know this is not so, because every human being has an infinite value and an eternal destiny in God: Jesus Christ died for every single one of us.
We are Christians when we can love not just “mankind” in the abstract, but each of the people around us. It is a sign of maturity to feel responsible for the well-being of future generations, but that mustn’t lead us to neglect opportunities to give ourselves and serve others in ordinary things: an act of kindness to those who work with us, genuine friendship shown in deeds, compassion for someone who is suffering or in need, even when their unhappiness seems slight in comparison with the great ideals we are pursuing.
Speaking of freedom, love for freedom, raises a difficult ideal which is one of the greatest riches of our faith. Because – let’s not kid ourselves – life isn’t a trashy novel. Christian fraternity isn’t something that comes down from heaven once and for all, but something that has to be built up day after day. It has to be built up in a life that keeps all its harshness, with clashes of interests, friction, struggles, in daily contact with people who seem unfair, and with unfairness on our part too.
But if that prospect discourages us, if we let our selfishness get the upper hand, or if we merely shrug our shoulders skeptically, that will be a sign that we need to go deeper into our faith, to contemplate Christ more. Because only in his school can we Christians learn to know ourselves and understand others, and live in such a way that we are Christ present among the people around us.