Unitarians, Universalists, and Unitarian-Universalists have always had a conflicted relationship with Christianity. Classical Unitarians and Universalists thought of themselves as Christians and represented themselves as such, but they were outnumbered by other Christians who disputed this claim, sometimes vociferously. From a religious studies standpoint outside of the fray, it seems obvious that these groups were indeed Christian, of a type (and all Christians are “of a type,” after all). So it reminds one of children who are biologically descended from someone but socially defined as “illegitimate”–they are indeed direct relations, but not acknowledged as such. Later on, many Christians were more willing to admit the Unitarians and Universalists were family members, yet by then some of these scorned children had decided they didn’t care whether they were part of the clan anyway. And now we have the situation of Unitarian-Universalists, whose religious structures, concerns, behavior patterns, and so on are consistently and obviously Christian to anyone who studies religious traditions that come from outside the West, yet who refuse to admit such continuing close relationship. Now it seems like a situation of minors who get legally emancipated from their parents–they are still directly related, but socially they are determined to have severed that relationship and become free entities.
All of this makes for fascinating (and at times headaching) work for religious studies scholars, who, like other social scientists, thrive on classification. If you ask an average UU if they are Christian, the response is likely to be “no.” Yet if you ask the average member of any religion other than Christianity/UUism if UUs are Christian, the response is likely to be “yes,” because the things that separate them seem miniscule compared to the things they share (especially when lined up against the things that separate them from any other major religion).
This seems to point to a problem with the word “Christian” itself. We should not confine it’s definition to merely the self-representational one. One solution for scholars might be to use the word in a very strict, contextual sense. This would entail rejecting the use of the word “Christian” as a noun in relation to the average UU. For simplicity’s sake, we’ll use the first definitions supplied by Dictionary.com. The noun definition of Christian is “a person who believes in Jesus Christ; an adherent of Christianity.” You would not point out a random UU and say “He is a Christian.”
However, the word Christian could be meaningfully employed as an adjective. The adjectival defintion of Christian is “of, pertaining to, or derived from Jesus Christ or his teachings.” You could point at a UU church and describe it as Christian from a sociological or cultural perspective. There is no doubt that UUism was “derived from Jesus Christ or his teachings” (and especially from the religious forms that grew up around those teachings).
So, is Unitarian-Universalism Christian? Arguably, it all depends on the context in which the question is asked.