Pluralism in a normative sense (as opposed to pluralism as a matter of description which is irrelevant for the purposes of this discussion) means valuing subjectivity over objectivity by declaring all cultural viewpoints (including religious viewpoints as a facet of culture) equally and fundamentally valid. The problems with this popular viewpoint-framework include first, that pluralism is itself a value that undermines all other values, and second, that it generally fails to be subject to its own scrutiny.
The value of pluralism is not somehow self-evident, regardless of whether it is treated as such. Even if it can be justified by rhetoric or evidence, pluralism is itself a value. The problem is that it is a value that undermines all other values. If I ascribe to pluralism, I cannot at the same time hold any other values, because that would be an assertion that those values were somehow true or the best or the most valid, which is inconsistent with pluralism. In fact, under the rubric of pluralism, there is no need to hold any other values at all: if all values are equally valid then no value supersedes another, and all values are thus also equally invalid. Pluralism, in its admirable desire for fairness and equity, swallows up everything else.
Furthermore, in practice, pluralism generally fails to live up to its own mandate. Most pluralists reject exclusivist or fundamentalist viewpoints. In other words, to the pluralist, all viewpoints are equally valid except for when they undermine pluralism itself. Thus all viewpoints actually aren’t equally valid because no viewpoint other than pluralism can ever be valid, since any statement of value necessarily implies the non-validity of contradictory values. Thus, under the rubric of pluralism, no value is valid because all values other than pluralism denigrate other values by not recognizing their equal worth and validity. But that is not even true: in fact, under the rubric of pluralism, no value is valid at all, not even pluralism, because rejecting say, Fundamentalist Christianity in the name of pluralism means recognizing that the pluralism is more valid than Fundamentalist Christianity, a situation that is impossible under pluralism.
Thus pluralism is undesirable as a stance because it not only undermines all other values, but in practice, pluralism even undermines itself. It is subjectivity taken to the logical, but absurd end. This end means the inability to make moral judgments of any kind, because it results in the rejection of all Ought principles. Even if not taken to the extreme, pluralism undermines strong Ought principles conceptually and thus undermines all moral imperatives, i.e., all statements of Should.
This lies at the heart of my unease with liberalism, at least liberalism as commonly articulated in America today. Liberalism is all passion but no principle. Certainly liberals have articulated a significant number of values couched in moral terms, and many liberals are extremely passionate about these values. But the problem is that liberalism includes and embraces pluralism as not just a value, but as a fundamental premise, and so liberalism fails to be able to articulate reasons for its values without rejecting a premise that it is unwilling to reject.
American conservatives, by contrast, get the force for their Ought statements from their belief in Christianity, pragmatism, or market economics. I may not agree with their Ought statements, or even acknowledge the validity of their sources, but they are articulating policies based on principles that are at least alleged to be objective. If you acknowledge even the possible validity of the source and the derivation of the Ought, then their Should-conclusions have a great deal of moral force. I’m not entirely sure about the source of libertarians’ Ought-principles.
Now, to be fair, many people are proponents of the same causes as liberals without being liberals in the sense that I am using it. For example, the Archbishop of Canterbury is socially progressive but theologically conservative. His Ought-principles, whether they are true or misguided, come from a set of objective moral standards. Ditto for my friend Bryant: as a faithful Mormon, he believes in absolute morality and objective values, but he concludes that those values—that set of Ought-principles—lead him basically to the same Should-imperatives that liberals advocate.
However, people like Bryant occupy a perilous place in the American left. Because their moral reasoning is based on objective standards, by definition they reject full cultural pluralism, which means they are treated with suspicion by fellow-liberals. It’s not always easy being both religious and a Democrat in the United States: conservatives think that your Progressive politics is a betrayal of your religion (because you derive a different set of Ought-principles from what is ostensibly the same source), and too many liberals think that your objective values are the antithesis of pluralism and thus inherently invalid (and since pluralism is fundamental to liberalism, your objective values are the antithesis of liberalism even if you advocate the same set of policy goals; the feeling is that you happen by lucky coincidence to advocate the same policy goals in one particular instance, but since you reject pluralism you can’t really be counted on).
Yes, I know that political reality means that Democratic candidates have to use religious talk to get elected. But it is also true that they suffer derision and scorn from liberals when they do. This is because for the kind of liberal I am talking about, anything that even potentially undermines pluralism is the mark of the enemy.