The "modern myth of separation," Professor Hamburger writes, "omits any discussion of nativist sentiment in America and, above all, omits any mention of the Ku Klux Klan," which made separation of church and state a central element in its anti-Catholicism. The Klan "exerted profound political power in states across the country and, probably more than any other national group" in the first half of the 20th century, "drew Americans to the principle of separation," Professor Hamburger writes.
As the author points out in Steinfels' column, the negative forces attached to promoting an idea do not invalidate the idea itself. After all, Nativist and racist sentiment was also an important element of the women's suffrage movement in the US as well - the votes of white women were necessary, it was claimed by some proponents, to offset the impact of the votes of Blacks and recent European (mostly Catholic and Jewish) immigrants.
But an honest debate calls for an honest account of motives, then and now.