The Unitarians weren't alsways the way they are now. I could be wrong, I am willing to admit it when I am, but twenty years ago, I read the history of the Unitarian movement.
I seem to recall that they were a group of believers who were tired of the bickering among Christian religious sects. In response, they decided to unify and accept basic premises. Unfortunately, those basic premises threatened to cause dis-unity, so they agreed to have certain rules to determine what is truth.
That denegrated to be only what can be proven as true. This narrowed to be only what could scientifically be proven as true. And that is what became of the Unitarian movement twenty years ago, but it wasn't always a group that rejected Jesus as the Christ.
It seems that the Unitarians are now accepting every hair-brained idea of religion EXCEPT fundamentalist Christianity.
I would recommand you read Servetus' works... You would be surprised (there is also a very good book about him and his books, Out of the Flames by Lawrence and Nancy Goldstone, quite recent...)