Back to the "syncretic" argument: I was reading a sermon by A. Powell Davies, a famous Unitarian minister, and this passage brought me back to this thread:
"To Unitarians, also, the brotherhood of man is not restricted, whether by nation, race or creed. This means that the...
There is a recognized group within the UU association known as the UUCF or UU Christian Fellowship. They encourage UU churches to retain more of their traditional Christian identity, and hold communion services at the UU General Assembly.