It behoves all men to consider whether that intelligence & piety and virtue in the great body of the people, upon which we have all acknowledged our whole security to depend, has not failed our expectations & disappointed all our hopes. We in this age are more unfortunate in one respect than the ancient gentiles. Among them the philosophers were divided into numerous sects—the folowers of Socrates of Plato of Pythagoras & of Zeno as well as of Epicurus. All the former had a mixture of good morals, manly virtues & true opinions among their errors & all of them served to counterpoise & counteract the poisonous pestilential & most fatal doctrine of Epicurus. The portico for example produced men like the Catoes, Cicero, Seneca, Brutus, Epictetus and others who were saints in comparison of Caesar and Anthony. But our modern philosophers are all the low grovelling disciples of Epicurus: Not one Stoick no Platonician among them. Where then are we going! Are we all to become Epicuri de grege porci?
John Adams to John Rogers, 6 February 1801. Pinning down what people mean by 'Epicurean' in the modern period is not an easy task, but Adams is likely thinking especially of Thomas Jefferson and his supporters, to whom he had just lost an election. In a different letter to Benjamin Rush, he identifies what he probably has in mind as the problem with Epicureanism: "banishing all Ideas of God, or Gods, of future Rewards and Punishments and of moral Government or Providence in the Universe, every Man may get into an habit of taking pleasure in ever Thing".
The emphasis in the letter to Rush on moral providence sounds Butler-esque, which led me to ask whether Adams had studied Butler, and, indeed, it turns out that he read Butler quite closely in college in 1756, since his diary for that year explicitly mentions his reading and is full of comments on matters related to themes in Butler and Richard Bentley. And Abigail Adams occasionally refers to Butler, as well, and recommends him to her son Charles. (Incidentally, an odd feature of the references for these online letters is that whenever Butler is referred to, the footnotes point to the Analogy. But outside the 1756 references, the references made by the Adamses are usually to the Fifteen Sermons.)