Adams thought Dupuis was a fiercely learned man whose criticisms needed answers. Of course, orthodox Christianity of either the Roman Catholic or Protestant bent would defend their faith with answers.
But with rare exception, Adams didn't want their answers. Rather he saw their corruptions as part of the problem that gave the Dupuises of the world reasons to attack Christianity. So instead he looked to fellow unitarians, namely Joseph Priestley, Thomas Jefferson and Francis Van Der Kemp.
Adams also positively mentions two other sources he found useful for his preferred project. One was the Bollandists who wrote the Acta Sanctorum, which Adams didn't read until around 1815. The Acta Sanctorum was as Adams termed it, a compilation of "Legends, of the Lives and Writings of the Saints and even of the Fathers, and of Ecclesiastical History in general."
The other was English clergyman Conyers Middleton, whose work Adams had been familiar with much earlier. His original work attacked chiefly the Roman Catholic Church but left the impression in the minds of some of implicitly attacking the orthodox Protestant dogma institutionally ingrained in England. Originally, provided such institutional Protestantism could believe Middleton's work a mere attack on the Roman Catholicism they rejected, they could endorse it.
But then later as he became more explicit, Middleton got in trouble with such Protestants in England. As this source informs:
He had meanwhile got into a controversy with Waterland. Waterland had attacked Matthew Tindal's ‘Christianity as old as the Creation’ (1730), which marked the culmination of the deist controversy. Middleton published an anonymous ‘Letter to Waterland,’ urging that apologists placed themselves in a false position by endeavouring to maintain the historical accuracy of every statement in the Bible. He ridiculed some parts of the book of Genesis, and said that Tindal should be answered by proving the utility of a traditional religion, and confuting his à priori theories of the ‘religion of nature.’ This sceptical tendency, really latent in the ‘Letter from Rome,’ now became obvious. Zachary Pearce [q. v.], afterwards bishop of Rochester, accused him in a ‘Reply’ of covert infidelity. Middleton's authorship had become known, and he was threatened with a loss of his Cambridge degrees. Middleton replied in two pamphlets, making such explanations as he could. Some time later (1733), however, an anonymous pamphlet by Dr. Williams, the public orator, declared that his books ought to be burnt and himself banished from the university, unless he made a recantation.One of the offending quotations of Middleton's is as follows: "[T]hat every single passage of the Scriptures, we call Canonical, must needs be received, as the very word and as the voice of God himself."
This post at American Creation written by a guest blogger contains research showing Adams became interested in this fight and ended up siding in favor of Middleton and against Waterland. In the meantime, it features the following quotation showing Adams doubted the veracity of the Epistle to the Hebrews:
But the question recurs, why was the original destroyed? What suspicions of interpolation, and indeed of fabrication, might be confuted if we had the originals! In an age or in ages when fraud, forgery, and perjury were considered as lawful means of propagating truth by philosophers, legislators, and theologians, what may not be suspected?This was a marginal note in John Disney’s Memoirs (1785) of Arthur Sykes. See Zoltán Haraszti, Prophets of Progress, 296. See also James H. Hutson, The Founders on Religion, p. 26.
(Jefferson would claim to Adams in 1813 that Middleton and Priestley were the basis of his own faith.)
And here in this 1813 letter to Jefferson, Adams puts together his understanding of Dupuis, Priestley and Middleton:
Dr Priestley pronounced [Dupuis] an Atheist, and his Work “The Ni Plus ultra of Infidelity.” Priestly agrees with him that the History of the Fall of Adam and Eve, is “an Alegory,” a Fable, [and] an Arabian Tale, and so does Dr Middleton, to account for the origin of Evil; which however it does not[.]And in his 1814 letter to Francis Van Der Kemp, Adams puts together Priestley, Middleton and the Acta Sanctorum:
I know nothing of Th. Browns popular Errors. Enfield contains enough. The Acta Sanctorum in 47 Volumes in Folio contains a pretty Specimen of them. Dr Middletons Works, the Model of Priestleys, without his excentricities, are a fine Sample.And invoking his old friend and mentor the unitarian Richard Cranch, Adams' letter to Van Der Kemp ends in a bang:
When I was a Boy, I wrote a Letter to my Friend Cranch more than 60 years ago in which this Globe was asserted to be the Bedlam of the Universe, into which all the insane, in Mercury Venus and Mars &c &c &c, were Sent to be cured or confined.
Neither The Acta Sanctorum nor Priestley nor Middleton nor Bruker nor the 18th nor the 19th Century have confuted my juvenile Hypothesis.