There are several varieties of Religious Pluralism
. Pluralism, as you may know, is an objection to religious exclusivism
(though there is a wide range of exclusivists all the way to inclusionist
Extreme Pluralism: the view that all religious beliefs are equally valid and true. You could dismiss this easily, as many religions have incompatible beliefs, ie. Monotheism versus Polytheism. Anthony Wallace, an anthropologist, estimated that in 10,000 years, there have been at least 100,000 religions. Two contradicting claims cannot both be true, so most people reject this.
Fundamental Teachings Pluralism: the view that the essential teachings of all major religions are true. Not all the beliefs, mind you, but the essential ones. Not everyone agrees on whether you can eat pork or whether purgatory exists, but there is a shared belief in a Supreme Being, piety and virtue, and an afterlife where justice is meted out. The problem with this idea is people can't seem to draw the line on what is "fundamental" in beliefs. Christianity believes in the Trinity, Islam and Judaism don't. Theravada Buddhists believe that there is no personal God. However, no religion allows murder.
Cafeteria Pluralism: the view that religious truth lies in a mix and combination of beliefs drawn from many different religions. This is becoming popular and new-age; people pick and choose beliefs from many different religious traditions. It's attractive to many people who are uncomfortable with the religion in which they were raised. There are two main problems with this. First, doctrines don't work well outside the framework they were created in. Reincarnation doesn't mesh with Christianity or Islam, both of which believe in a Judgement Day. Second, even if you mix the beliefs, why should you or anyone else think that those beliefs are true? Most contemporary theologians agree that few specific religious doctrines can be rationally justified without referring to divine revelation. It's just wishful thinking; would God really scatter His revelations to the children of Israel and the Hindus? The Muslims argue that both received nearly identical Revelation but were corrupted over time. Other than personal religious experience, people can't really claim that their personal beliefs mix is the Truth and everyone else is mistaken.
Transcendental Pluralism: the view that all major religious traditions are in contact with the same ultimate divine reality, but this reality is experienced and conceptualized differently within these various traditions. Recently John Hick defended this in 1989. He admits that the religions cannot all be true, there is too much contradiction. However, he argues that there is an important sense in which all the great religions are equally valid and true. His idea is supposed to use Kant's distinctions between things as they exist and how we perceive them. Thus, God (the Ultimate Reality) is transcendent and ineffable. People perceive it through different lenses; some see Him as personal, some focus on Him being absolute. Hick concluded that all the great religions are equally valid and true, because he felt they were all in touch with God and the Reality, and were all equally effective paths to salvation. However, this has many problems; one cannot say that God is both one and many, both the Sustainer and not the Sustainer. Can you believe that your religion is nothing but myths but conducive to relating to God properly? Can you still be "Christian" if you don't believe in any of its unique tenets? Alvin Plantinga pointed out that Hick's over-broad definition seems impossible without doublethink or bad faith; you would have to accept that your religion's beliefs are no more true than any other, yet you still cling to it for some sort of benefit.
Religious pluralism is more of a postulate; it is quite difficult to prove that no religion is closer to the truth than others. Often it is a reaction against "hard exclusivists" who argue that salvation and reality are found in only a single religion. "Soft exclusivists" or inclusivists believe that one religion has it mostly or completely right and all other religions go seriously wrong. They often admit that salvation can occur outside their faith, prompting some to label them "inclusionists." This standpoint is the most common form of "exclusivism" today. I suppose Religion is much like politics, you can believe in a single party, or take a more bipartisan stance. If there is no knockdown argument to convince you to join a certain party, what is there to do? A pluralist may argue to give up being on that side, but they rarely produce an argument to prove that nobody is closer to the truth than others.
Gregory Bassham's essay "The Religion of The Matrix and the Problems of Pluralism", in the book The Matrix and Philosophy, by William Irwin