Razib Khan dusts off some religious history books:
I agree with Winnifred Sullivan’s argument in The Impossibility of Religious Freedom that one of the ways in which the American religious injunction toward neutrality was made practicable was that religion qua religion was fundamentally shaped by a belief-centric (orthodoxy) Protestant model. Why did Roman Catholicism and Judaism not change that model? Because both of these religions in the United States were heavily “Protestantized.”
The vast majority of American Jews do not adhere to the orthopraxy, a system of behaviors and actions, which defined Judaism for nearly 1,500 years. Rather, their Judaism is defined by an unadorned monotheism, a small set of rituals, holidays and taboos, and a “culture.” Similarly, American Catholics are very hard to differentiate from mainline Protestants in their beliefs & practices; the Americanist won over the long haul. In fact, they would no doubt be shocked at how Protestant American Catholics had become in their outlook.