I just listened to the most recent podcast from The Religious Studies Project, a discussion about secularism with Donovan Schaefer. Schaefer introduced an interesting perspective (between 13:03 and 16:33):
…Secularism is itself a particular iteration of Protestant Christianity, that we have the version of secularism that we have because we are an offshoot of a cultural/historical context that defined religion in a particular way…. It's precisely because we see religion as something that is potentially private, individualized, and belief-oriented that religion is something that can be relegated to the private sphere and therefore secularized according to the conventional definition…. Religion gets defined as something that is personal rather than corporate…. All of these details of Protestantism…make up the coordinates of what eventually becomes secularism…. Secularism as something that Christianity does in exactly the same way that…you would talk about the great schisms—Orthodoxy from Catcholicism, Protestantism from Catholicism—and then also could locate secularism as, in a sense, another schism, as another permutation of Christianity that is part of the story of Christianity as a world religion (emphasis added).
In the sociology of religion, secularization is generally framed as a break from religion; in this framing, however, secularization is the continuation of religion. Cool stuff!