Reason, justice, & equity never had weight enough on the face of the earth to govern the councils of men. It is interest alone which does it, and it is interest alone which can be trusted.Shades of Adam Smith:
It is not from the benevolence of the butcher, the brewer, or the baker that we expect our dinner, but from their regard to their own interest.Which is from Wealth of Nations, published in March of 1776. So did John Adams get his hands on an early copy of Wealth of Nations between its publication in Britain in March and the debate in America in July. Possible but I suspect that this was an example of great minds with parallel thoughts.
It would be easy to speculate that to some degree both renditions are a development of the traditional Latin question, "Cui bono?" (Who benefits?) attributed to Lucius Cassius Longinus Ravilla, a Roman consul in 127 BC.
Adams' larger point is as true today as it was 240 years ago. People answer a lot more diligently to incentives and their interests than they guide their actions and decisions by reason, justice, and equity.