Hovering like a stern schoolmarm over much of our political discourse and decision-making is a sort of lurking censor, monitoring political decisions to ensure that they are based on “secular” grounds and purposes. Let us call this regulator “the secularism constraint.”
In many cultural neighborhoods, the secularism constraint seems almost as natural and ineluctable as the law of gravity. Legal scholars and political theorists argue for one or another variant of the constraint (a/k/a “public reason”), or more often just take it for granted. Constitutional doctrine– the so-called Lemon test, from the case of Lemon v. Kurtzman (1971)– provides at least ambiguous validation with its “secular purpose” requirement for government action.