I agree there has always been and will always be a political component to religion. I also think it’s difficult at best and impossible at worst to completely separate our beliefs, be they religious or secular, from our politics. Whether we embrace human rights as people of faith or embrace them as Humanists, the language we use to express these convictions in the political realm will always be colored by the theology and/or philosophy we identify with.
I also agree that Enlightenment Humanism didn’t arise in a vacuum. As the historian, Larry Siedentop argues in his book Inventing the Individual: The Origins of Western Liberalism, Christianity’s emphasis on the importance of each individual’s soul was critical to the development of our modern views of individuality. One need not believe in traditional Christian notions of the soul or salvation to have benefited from this history.
That said, Christianity does not have a history of embracing pluralism. It just helped to pave the way for it in spite of itself. Nor does monotheism more broadly. What set the Abrahamic religions apart from paganism was, among other things, their conviction that they had the “one true god.” While the Vatican in the 16th century was extremely concerned with each individual soul, it was also concerned with power and was not willing to concede to the Protestants or anyone else that there was any avenue a soul could follow to heaven that did not go through the Catholic Church.
While Christian concern for the value and uniqueness of each individual soul in the eyes of God helped create an environment for modern liberal notions of individuality to emerge, so did the 100 years of religious warfare that tore Europe apart following the Reformation. Enlightenment ideals of pluralism were also very much a reaction to this century of religious conflict.
So, to make a potentially long response a bit shorter, I would argue that Humanistic values are indeed currently ascendant and we all have an interest in keeping it that way. These values are only in conflict with religion in so far as religion resists pluralism. I don’t think a contemporary American liberal or progressive, be they religious or not, has any reason to quarrel with Humanism. Pluralism is a defining feature of modern liberalism, but first, it was a fundamental Humanist value. It was as such that it found its way into the US Constitution. Humanism’s embrace of religious liberty in the form of individual choice is what enables religious diversity to thrive. Left to their own devices most religions tend to prefer a theocracy over democracy. Only a state that favors religious liberty but no particular faith can keep these tendencies in check, thereby facilitating each person’s freedom to worship or not as they see fit.
That said, I’m an unapologetic Humanist :-)