Stross notes that as with all religion, those sects with most in common are the ones who hold the most vicious grudges against one another. 'Is that clear?'"
The "grudges" that most Christian denominations hold against each other, if one can even call them grudges by now, are by and large substantially less the fighting over operating systems by geeks. The Catholics officially regard baptized Protestants as Catholics who are out of communion with Rome. The term is "separated brethren," not "those damn heretics" now. Likewise, most Protestant denominations, even conservative ones, may harshly criticize the Catholic Church on issues of doctrine but regard observant Catholics as fellow Christians. The level of animosity is significantly less except on the outliers than Stross realizes, but then as far as I know he's an atheist and like most atheists he tends to think far too highly of his knowledge of religion especially Christianity.