Not because, remember, people tend to assume that religious fundamentalist revolts would necessarily enter into an alliance with "the evil ones" of OTL. Establish that the Union, which is always considered the good and just side that launched a moral crusade in the name of abolitionism (no matter how contradicted the evidence of the time is), is at the same time the side of the murderous religious fundamentalists , it would be more or less like postulating that the Imperial Japanese Army was actually fighting for the independence and freedom of the Asian peoples instead of fighting in order to being the new colonial lord.