Decades after the civil war, southern organizations like the daughters of the confederacy started a massive propaganda effort to whitewash the southern cause and make slavery seem like a benign institution. This came after southern terrorists had been successful at forcing federal troops to leave the south in the late 1870s so that they could go around murdering any black people who tried to organize themselves politically. Racism was a political tool, by pushing racist narratives they could promote a political agenda at home and by promoting those views around the country they could avoid a backlash for making a farce of democracy. It was not inevitable that this campaign of organized racism would win, occasionally white populists in the south tried to ally themselves with black people. They failed because of the effectiveness of the campaign to disenfranchise the blacks but it wasn't a foregone conclusion that they would fail.
If the CSA had survived, it would have continued to practice chattel slavery for decades, well into the era of photography and the explosion of newspaper correspondents. Their efforts to depict slavery as a benevolent institution would have been as hollow as the Soviet efforts to claim their workers were more free then american workers. Just like the anti-communists used images of soviet breadlines, the anti-racists would use images of confederate chain gangs. The desire for magnanimity towards one's countrymen that gave tolerance to confederate apologists would have been completely absent. Black people from the south would be known as refugees, not fugitives. And while race relations in the north were never good before the civil war, they were certainly far less racist then the south. Things would have certainly been far more progressive.