On the Virgin Mary and the Trinity:
If I understand the Doctrine, it is, that if God the first second or third or all three together are united with or in a Man, the whole Animal becomes a God and his Mother is the Mother of God.
It grieves me: it shocks me to write in this stile upon a subject the most adorable that any finite Intelligence can contemplate or embrace: but if ever Mankind are to be superior to the Brutes, sacerdotal Impostures must be exposed.
John Adams to Francis van der Kemp, October 23, 1816, Adams Papers (microfilm), reel 122, Library of Congress.
It's interesting that Jefferson and Adams did not believe that the Trinity is a harmless irrationality, but a corrupting and dangerous irrationality. They were militant anti-Trinitarians.