There are significant sources of religious resistance to religious pluralism. The most prominent examples on the American religious scene are Evangelicals and Fundamentalists. Granted Fundamentalists express a more extreme measure of anti-pluralism, Evangelicals generally inhere to the denial of authentic spirituality outside of a personally actualized Christiology. That is, unless one has "accepted Christ" as a personal savior, it is deemed impossible to actually know God. Hence, Evangelicals and Fundamentalists consider Jews and Muslims (their religious near-of-kin) to be as Hell-bound as any other for their non-acceptance of Christ.
How does atheism fit into religious pluralism? Is not atheism more akin to fundamentalism for its intolerance of heterogeneous ideas about metaphysical realities? Can atheism fit into the fabric of religious pluralism? Should it even desire to do so? I do not have the definitive answers to these questions, but I would like to propose some.
I consider God a metaphor, a symbol. I consider God a symbol, albeit one of several of humanity's search for meaning. God has been one venue through which people have sought to ascribe meaning to their lives and to humanity's existence. However, other such ascriptions exist including Zeus, Odin, or El. All of these today are understood to be mythological and non-historical. However mythological they may have been, their personas influenced the lives and directions of people under their spell--both negatively and positively. Today we can see them as a metaphor for the personality that people often ascribed to the machinations of apparent fate and the functions of nature.
Atheism is not an utter and total cap on human spirituality. Several authors have explored approaches to human spirituality and spiritual actualization in a post-deity existence. Some of my favorites include Thomas Berry and Comte-Sponville. For them, spirituality is not a matter of worshiping other beings or communing with numens, rather it relates to interconnectedness, meaningfulness, and transcendence. It is understanding the immensity of the cosmos and the negligible existence of Earth as a sacred and safe harbor for life. It is likewise understanding that humanity is a product of the cosmos, made from from star dust--the heavy elements produced by stars like our own sun.
Sam Harris in his work The End of Faith posits a spiritual pathway for atheists as well. This pathway relates to meditation on the limitations and boundaries of human perception and knowledge. Some have criticized Harris for developing a sort of New-Age spirituality for atheists; however, it is worth noting that he has put forth the effort.
Though atheism does militate against the literal existences of deities, it does not necessarily obviate against some forms of human spirituality. Though the atheist may view the pneumatic experiences of those embedded in theistic religious traditions differently, the atheist need not deny that the believer has an authentic experience or benefit in her religious tradition. Though the atheist might understand the believer's experience to be the result of purely psycho-chemical phenomenon, the deity-as-metaphor paradigm would allow her to embrace the believer in her faith. If the matter were only this simple, I would assert, then, that the atheist could contribute to and participate in religious pluralism.
There are pernicious forms of religion that do more damage to science, cultures, the environment, politics, and to human rights than are worth countenancing. Fortunately, these religious paradigms are the same that are adverse to religious pluralism. They are, to use the description of Dennet, "sugar religions." I will leave the reader to reflect on the above and tear it apart as I am sure that I need some constructive feedback.