Yeah, but the "At some point" is the rub. How long? Even after the war, Christian leaders like R.L. Dabney were publishing biblical defenses of slavery, and the confederate constitution specifically forbade that government from outlawing the peculiar institution.
To argue about "what point" is pretty pointless, given that the WBTS was not fought to free slaves. The "point" could have been 1800, 1835, 1920 --- pick a year. The real point is, that it is a fallacy to believe that slavery in the US would have continued indefinitely -- making it the only western country to do so. And the last time I checked, there was nothing that prevented the CSA constitution from being amended.