The constitution was written for a moral and religious people. It is wholly inadequate for any other.
John Adams
On the other hand, here is what John Adams actually wrote. Not exactly a Pom Pom flailer for Christianity.
"The question before the human race is, whether the God of nature shall govern the world by his own laws, or whether priests and kings shall rule it by fictitious miracles?"
-- John Adams, letter to Thomas Jefferson, June 20, 1815
Regarding Government Meddling With Religion
"We should begin by setting conscience free. When all men of all religions ... shall enjoy equal liberty, property, and an equal chance for honors and power ... we may expect that improvements will be made in the human character and the state of society."
-- John Adams, letter to Dr. Price, April 8, 1785
"I shall have liberty to think for myself without molesting others or being molested myself".
-- John Adams, letter to his brother-in-law, Richard Cranch, August 29, 1756
Regarding Religion Meddling with Government
"We think ourselves possessed, or, at least, we boast that we are so, of liberty of conscience on all subjects, and of the right of free inquiry and private judgment in all cases, and yet how far are we from these exalted privileges in fact! There exists, I believe, throughout the whole Christian world, a law which makes it blasphemy to deny or doubt the divine inspiration of all the books of the Old and New Testaments, from Genesis to Revelations. In most countries of Europe it is punished by fire at the stake, or the rack, or the wheel. In England itself it is punished by boring through the tongue with a red-hot poker. In America it is not better; even in our own Massachusetts, which I believe, upon the whole, is as temperate and moderate in religious zeal as most of the States, a law was made in the latter end of the last century, repealing the cruel punishments of the former laws, but substituting fine and imprisonment upon all those blasphemers upon any book of the Old Testament or New. Now, what free inquiry, when a writer must surely encounter the risk of fine or imprisonment for adducing any argument for investigating into the divine authority of those books? Who would run the risk of translating Dupuis? But I cannot enlarge upon this subject, though I have it much at heart. I think such laws a great embarrassment, great obstructions to the improvement of the human mind. Books that cannot bear examination, certainly ought not to be established as divine inspiration by penal laws. It is true, few persons appear desirous to put such laws in execution, and it is also true that some few persons are hardy enough to venture to depart from them. But as long as they continue in force as laws, the human mind must make an awkward and clumsy progress in its investigations. I wish they were repealed. The substance and essence of Christianity, as I understand it, is eternal and unchangeable, and will bear examination forever, but it has been mixed with extraneous ingredients, which I think will not bear examination, and they ought to be separated. Adieu."
-- John Adams, one of his last letters to Thomas Jefferson, January 23, 1825. Adams was 90, Jefferson 81 at the time; both died on July 4th of the following year, on the 50th anniversary of the signing of the Declaration of Independence.
"Thirteen governments [of the original states] thus founded on the natural authority of the people alone, without a pretense of miracle or mystery, and which are destined to spread over the northern part of that whole quarter of the globe, are a great point gained in favor of the rights of mankind."
-- John Adams, "A Defense of the Constitutions of Government of the United States of America"
Prophetic Statements Based on History
"The priesthood have, in all ancient nations, nearly monopolized learning.... And, even since the Reformation, when or where has existed a Protestant or dissenting sect who would tolerate A FREE INQUIRY? The blackest billingsgate, the most ungentlemanly insolence, the most yahooish brutality is patiently endured, countenanced, propagated, and applauded. But touch a solemn truth in collision with a dogma of a sect, though capable of the clearest proof, and you will soon find you have disturbed a nest, and the hornets will swarm about your legs and hands, and fly into your face and eyes."
-- John Adams, letter to John Taylor, 1814
But Hey, Don't Hold Back.
"Numberless have been the systems of iniquity The most refined, sublime, extensive, and astonishing constitution of policy that ever was conceived by the mind of man was framed by the Romish clergy for the aggrandizement of their own Order They even persuaded mankind to believe, faithfully and undoubtingly, that God Almighty had entrusted them with the keys of heaven, whose gates they might open and close at pleasure ... with authority to license all sorts of sins and Crimes ... or withholding the rain of heaven and the beams of the sun; with the management of earthquakes, pestilence, and famine; nay, with the mysterious, awful, incomprehensible power of creating out of bread and wine the flesh and blood of God himself. All these opinions they were enabled to spread and rivet among the people by reducing their minds to a state of sordid ignorance and staring timidity, and by infusing into them a religious horror of letters and knowledge. Thus was human nature chained fast for ages in a cruel, shameful, and deplorable servitude....
Of all the nonsense and delusion which had ever passed through the mind of man, none had ever been more extravagant than the notions of absolutions, indelible characters, uninterrupted successions, and the rest of those fantastical ideas, derived from the canon law, which had thrown such a glare of mystery, sanctity, reverence, and right reverend eminence and holiness around the idea of a priest as no mortal could deserve ... the ridiculous fancies of sanctified effluvia from episcopal fingers."
-- John Adams, "A Dissertation on the Canon and the Feudal Law," printed in the Boston Gazette, August 1765
"The Church of Rome has made it an article of faith that no man can be saved out of their church, and all other religious sects approach this dreadful opinion in proportion to their ignorance, and the influence of ignorant or wicked priests."
-- John Adams, Diary and Autobiography