You are conflating various views that eventually became “Unitarianism” with the word “unitarianism”. Unitarianism combined several heretical doctrines besides having a similar sort of Christology as, say Arians. Unitarians, for example, rejected the notion of original sin. But one of the biggest mistakes people make is that they somehow think that what passes for Unitarianism today is what it was originally.
Unitarians claimed that they were Christian, and the arguments that others had with them were over matters of systematic theology that historically fell within Christian boundaries. It was only a very long time later that Unitarianism morphed into essentially nothing (”What do you get when you cross a Jehovah’s Witness with a Unitarian? Someone who knocks on your door but isn’t quite sure why.”)In fact, the early Unitarians were very Old Testament oriented compared to modern evangelicals.
John Adams was a Bible thumping Christian (just read what he has to say about God and the Bible). He may have had a low Christology by 1800, but there is no evidence at all that he rejected Original Sin, etc. Again, there were no Unitarian signers of the Declaration - not Unitarian in the original meaning of the term, and certainly not in the modern meaning of the term.
Thanks for your informative post. I had a powerful hunch that the Unitarianism of today was not akin to that attributed (rightly or wrongly) to John Adams, a Founder whom I greatly esteem and who has not received the respect I think he is due, while Jefferson, who could be very sneaky and duplicitous, outranks him in the esteem of many FReepers. What others have posted here about Adams and his wife shows to me that Jesus would consider them “not far from the kingdom of God.” I.e. not quite there, but sincere in their beliefs. I know quite well that Adams believed that republican govt. would only survive in the context of a pious and reverent populace.