From Stark & Bainbridge’s The Future of Religion (1985), a seminal book in sociology of religion:
The South is overwhelmingly Protestant, and southern Protestantism is so overwhelmingly Baptist and Methodist that southerners have had little need to accommodate even many major Protestant denominations, let alone Catholics or Jews. Thus, anti-Semitism and anti-Catholicism are relatively common in the South, as they are in very Protestant areas outside the South.
It is not that Protestantism causes religious intolerance; religious intolerance is central to the entire Judeo-Christian tradition. It is not difficult to understand why religions holding that they alone possess the true faith are intolerant of “false” faiths. (Stark & Bainbridge, p. 90).