Consider a basic definition of pluralism provided by Google:
a condition or system in which two or more states, groups, principles, sources of authority, etc., coexist.
The definition has an ambiguity in the term coexist insofar as it can be understood positively — as is intended in the “Coexist” bumper sticker — or it can be understood in a neutral sense. In the neutral sense, any two things that exist simultaneously at a specified level can be considered a case of pluralism.
Pluralism isn’t inherently a good thing or bad thing. We can imagine a world in which two tribes exist on the same small island and where everything tribe α believes is good is believed to be evil by tribe β and the beliefs of each tribe are fixed. Bringing these tribes together under a single system wouldn’t just be impractical, it would be bad. Such a world would be a dystopia.
Now imagine a world in which two tribes exist on the same small island but the two tribes share the same beliefs about justice and the basic (or primary) goods and these beliefs are fixed. And let’s say that the two tribes, at both the group and individual level, have a diversity of skills and capacities. This is a case in which pluralism is good. Since the goods which exist are so numerous that no individual can practice all the goods he or she might, and since human capacities are so broad that no one can develop all of his or her capacities to their fullest extent, pluralism turns out to be (an additional) good in this world. Such a world would be a utopia.
The actual world is somewhere between these dystopian and utopian kinds of pluralism. There have been significant periods of (relative) peace and flourishing, but everyone with a modest knowledge of human history has felt Hobbes’s description of “the life of man” as “solitary, poor, nasty, brutish, and short” ring true. At the national level, nations have had certain ideological enemies and at times these ideological enemies have been powerful enough and determined enough that hot and cold wars were inevitable. Within nations, there have existed factional enemies where the differences in theories of justice have been sufficiently significant and entrenched such that civil wars were inevitable.
Christians should have no trouble acknowledging the fractured nature of the world and that, so long as this fracture exists, there will be various kinds of pluralism beyond our grasp:
“Do not be yoked together with those who do not believe. For what partnership is there between righteousness and lawlessness? Or what fellowship does light have with darkness? What agreement does Christ have with Belial? Or what does a believer have in common with an unbeliever?” — (2 Cor. 6:14–15)
The Bible urges Christians to pursue peace “with everyone” and, thus, a type of pluralism. But it does this with an acknowledgement that it may be beyond our grasp:
“If possible, as far as it depends on you, live at peace with everyone.” — (Rom. 12:18)
Interestingly, the exhortation in Romans 12 comes in the context of trusting in God to execute justice and the passage then focuses on the government as one of God’s instruments towards that end.
The point I’m driving at here is that pluralism qua pluralism can’t be the basis of national harmony. What would it mean to try to unite around the ideal of pluralism? This is like saying we should unify around the concept of unification. Some Christians often make the mistake of thinking that unity takes precedence over doctrinal or interdenominational differences, as though unity is its own highest end. But the Bible never urges this kind of unity. Rather, the Bible argues that we should be unified on the basis that we have a common savior and a common faith (doctrine). Where that commonality does not exist, separation is urged (cf. 1 Cor. 5 where separation in certain contexts is urged in the hopes of achieving unification).
But in regards to nations my claim is not fellow citizens should not make unity or pluralism its own good to be sought for its own sake, but that pluralism simply can’t function as its own good. It cannot, in itself, provide a stable basis for social harmony. We may coast along for some time under the idea that we’ll work together for the good of pluralism per se, but this is a psychological quirk masking other values that we are seeking (even if it is something as thin as economic security). David French’s Sunday essay “Yes, America Could Split Apart” seems to be using the language of pluralism to mask more robust common ground. Thus, French asks “Can we not pledge to protect [this nation as a] home [for our political opponents] by — at the very least — respecting their liberties and autonomy?”
The problem is that this more robust common ground — liberty and autonomy — is simply assumed to exist. A good case could be made that it does exist, but in a very precarious state. Our moral values are drifting ever apart. One example is in the transgender issue. For those committed to a certain ethic, it is child abuse to refuse to support your child’s wishes to be a different gender. For others, supporting your child’s wishes to be a different gender is child abuse. Whatever content we give to the terms “liberty” and “autonomy,” no one is seriously considering placing child abuse in those bins. Of course, it may be pointed out that those who have this level of commitment to transgenderism are a minority, only on the fringes. But the problem is not merely in things as they exist now — which would have been unimaginable fifty years ago — but the direction or trajectory of liberals and conservatives and the fact that both groups see their trajectory as good even if there is respective in-house disagreement over speed. (There is also the fact that while the those who are committed to radical transgenderism are relatively few, they hold significant power in culture-shaping institutions and few are willing to openly disagree with them.)
Maybe part of the disagreement between post-liberals and classical liberals stems from perspective: perhaps post-liberals are envisioning what sort of society we might wish to create and classical liberals are contemplating the society we have. Or maybe I’m wrong about that, but nevertheless the difference between the rules we might fight for when creating a society and the rules we might fight for when we a born into a society “mid-narrative” can lead to different strategies and immediate goals.
Finding ourselves mid-narrative will certainly require more flexibility and a far thinner pluralism than we might have wished for. Or, worst case, finding ourselves mid-narrative we may discover too little common ground as a basis for pluralism.
 The example of the coexistence bumper sticker has its own vagueness — as is unavoidable in any bumper sticker. Why is coexistence positive in this instance and not neutral? In the neutral sense, all these religions already coexist (and mostly do in the positive sense too). Regardless, it’s clear that the bumper sticker is attempting to encourage something — coexistence — because it is believed to be positive or good.
 cf. Book 13. Hobbes doesn’t wholly confine this to a state of nature in the abstract. If anyone doubts the truth of his statement, Hobbes challenges: “Let him therefore consider with himself, when taking a journey, he arms himself and seeks to go well accompanied; when going to sleep, he locks his doors; when even in his house, he locks his chests; and this when he knows there be laws and public officers armed to revenge all injuries shall be done him; what opinion he has of his fellow-subjects when he rides armed; of his fellow-citizens, when he locks his doors; and of his children and servants, when he locks his chests. Does he not there as much accuse mankind by his actions as I do by my words?”
 cf. Romans 12:18–13:7.