I almost shudder at the thought of alluding to the most fatal example of the abuses of grief which the history of mankind has preserved — the Cross. Consider what calamities that engine of grief has produced! With the rational respect that is due to it, knavish priests have added prostitutions of it, that fill or might fill the blackest and bloodiest pages of human history.

Letter to Thomas Jefferson (3 September 1816), published in Adams-Jefferson Letters: The Complete Correspondence Between Thomas Jefferson and Abigail and John Adams (UNC Press, 1988), p. 488