Note: I like Hamburger's book. I think it deserves much of the praise it got and that he is a top notch scholar. However that doesn't make it immune from criticism or serious error.
Jim Lindgren, no religious fanatic he (a self described atheist), and another top notch scholar (in my opinion; he wouldn't be blogging at Volokh if he weren't) has a post which peddles the weakest aspect of Philip Hamburger's work.
The following is an email I sent Prof. Lindgren. (I don’t expect a reply because I’ve sent him a few other emails over the years to which he didn’t reply):
In a general sense, I like Hamburger’s book and endorse the idea that “SOCAS” doesn’t properly vet constitutional religious rights, especially those that incorporate against state and local govts. I also think the research Hamburger et al. did with regards to the KKK and their anti-Catholic bias and endorsement of the separation principle is interesting.
However, to try to bring that up in an argument over the proper way to interpret the Constitution is weak. It’s the genetic fallacy/poisoning the well. And no, the evidence does not show Justice Black’s (or Rutledge’s) “Klan” mentality led them to decide the way they did in Everson.
Ed Brayton did a post on the matter a few years ago which raises a similar point.
I also noted on this First Things thread, this argument isn't just "poisoning the well"/the genetic fallacy, it's also a non-sequitur. That is, even IF Black was an anti-Roman Catholic bigot when Everson was decided, it doesn’t follow that he would deny Roman Catholics their religious rights.
John Adams was an anti-Catholic bigot, but, nonetheless believed in respecting the religious rights of Roman Catholics.
“I do not like the late Resurrection of the Jesuits. They have a General, now in Russia, in correspondence with the Jesuits in the U.S. who are more numerous than every body knows. Shall We not have Swarms of them here. In as many shapes and disguises as ever a King of Gypsies, Bamfield More Carew himself, assumed? In the shape of Printers, Editors, Writers School masters etc. I have lately read Pascalls Letters over again, and four Volumes of the History of the Jesuits. If ever any Congregation of Men could merit, eternal Perdition on Earth and in Hell, According to these Historians, though like Pascal true Catholicks, it is this Company of Loiola [Ignatius Loyola -- Ed.]. Our System however of Religious Liberty must afford them an Assylum. But if they do not put the Purity of our Elections to a severe Tryal, it will be a Wonder.”
- John Adams (1735-1826), Letter to Thomas Jefferson, May 6, 1816, quoted in The Founders on Religion: A Book of Quotations, James H. Hutson, editor (Princeton University Press: 2005), 44-45.