The main problem I see with the Sources is that they hide the theological dispute that has shaped contemporary Unitarian Universalism: the Humanist rebellion against liberal Protestantism, a historic event that happened throughout most of the 20th century.
As is true with all historic events, that Humanist Rebellion against Liberal Protestantism has a beginning, a middle, and an end. It is a story. It is, to a large extent, our story.
By simply listing brief summations of Humanism and Theism as differing options on a menu of theological perspectives, the Sources statement don't explain how their clash threatened to split liberal religion, and how that clash was defused and partially resolved.
I won't retell the whole story of the conflict, but will remind everyone that it was not a silly conflict. It was a serious dispute over the nature of reality that would define the teachings and liturgy of our religious communities. A lot was at stake: churches gained and lost members, ministers lost their careers, congregations were split. Beautiful stained glass windows were covered up or destroyed.
Ultimately, Unitarian Universalists moved toward a theology of pluralistic agnosticism about the propositions of formal theology. All opinions would be welcome, as no one really knows the whole truth. (The parable that best exemplifies the retreat from the battle lines is the story of the "Blind Men (sic) and the Elephant" which seemed to come into Unitarian thought with its re-telling by Sophia Lyon Fahs in "Long Ago and Many Lands" in 1948).
The Sources statement also exemplifies that Pluralistic Agnosticism: a menu of differing theological traditions that allows each person to pick and choose their truth.
The defusing the Humanist-Theist dispute by turning to Pluralistic Agnosticism had two major effects.
1. Pluralistic Agnosticism allowed UU's to acknowledge other spiritual and religious traditions beyond the binary of humanism and theism. These newly discovered, or re-discovered, and acknowledged influences are summed in the source statements about mysticism, world religions, and earth-centered spirituality. I suspect that as time goes on, more sources will be discovered and acknowledged in a statement of the influences on our living tradition: western Buddhism, Feminism.
2. But for all the growing diversity of theological influences on contemporary Unitarian Universalism, what unites UU's (as much as that is possible) is our public theology, as expressed in the Principles list, and in the 2nd Source: "words and deeds of prophetic people which challenge us to confront powers and structures of evil with justice, compassion, and the transforming power of love."
I wonder what value you would see in bringing the conflict forward in the minds of young UUs today -- especially in memorializing conflict, specifically, in our Sources and Principles statements.
Reading this post and the one before it gives me two feelings -- one, that the conflict that I thought settled amicably 50 or more years ago is actually still alive and still conflicted in at least some UU circles; and two, that both Christianity and Humanism are somehow privileged in UU thought more than the Buddhist, Earth-based, Hindu or Jewish thoughts that inform the congregation I am in today.
Tom, I defer to your far greater knowledge of Unitarian-Universalist history, and I have no doubt that Pluralistic Agnosticism (a mouthful but apt label) is the official position of the UUA, but I don't think that the Humanist-Theist dispute is completely resolved on the ground. By way of example, I still hear complaints about traditional religious language and music. People may not be covering up stained glass windows or firing ministers, but we also aren't all on the same page. I think there are folks in the pews who would prefer an exclusively humanist message from the pulpit.
This strand of humanism that focuses on its rejection and criticism of Christianity and other traditional beliefs, as opposed to a more positive focus, runs counter to what I perceive to be trends of thought among those who came of age in the 1970s and later. Around that time religious identity began to be perceived as similar to, if not identical to, more intrinsic types of identity. As a consequence, criticizing the beliefs of any religion (as opposed to criticizing the political positions inspired by religious beliefs) can sound intolerant regardless if whether the theology under scrutiny is powerful in this country like Christianity, or vulnerable like Islam and other minority faiths.