I can't speak to South Africa, but I can speak to the US. You have to break it down a bit by class -- elite whites would have talked about race differently than poor whites (just like today). Neither was "more racist" than the other but they would have spoken differently. Elite whites would sugar coat things, and lower income whites would be more willing to say it out loud.

Of course whites believed that that black folks were inferior and unfit to participate in government, but they would not have said it that way. They would have said "Its best for people to stick to their own kind." Just like today, white people back then did not see themselves as bad people. Most would not have claimed the title racist or admitted to hating black folks. But they did believe that black and white people were inherently different. Today we know race is not biological, and instead we blame culture. But otherwise racism works just like it always has.

The south created a criminal justice system meant to arrest and imprison black men (it had been a profit-making convict leasing system up until the 1920's). So White southerners looked at that and said, "Black men are prone to criminality, we have to keep society safe from that threat." They saw their own sons as "sowing some wild oats" when they got in trouble, but a black teenager doing the same thing was a threat to society. They would say that black men were prone to crime and violence, and especially violence against white women. That's why false accusations of sexual misdeeds or forwardness towards white women was so often used to justify lynching. Segregation was seen to be necessary to protected white women from black men.

Even though black communities had middle class business owners, teachers, preachers, etc, most black women worked as domestic laborers and most black men did physical labor and farming. So the whites looked at the majority of black folks who were poor and said, "Look they are lazy and unintelligent, they are suited for these kinds of jobs."

They took that attitude to government and argued a kind of white man's burden, "Whites should govern because we know best what it good for everyone." They convinced themselves that "separate but equal" was actually equal even though it wasn't. So in terms of government, white folks would say "if you gave black folks the right to vote and participate equally in government, they wouldn't know how to do it right, eventually they would want to end segregation, and before long you would have rapacious young black men sitting next to innocent white girls in classrooms."

Human beings are really good at convincing ourselves that we are not oppressing people even when we clearly are.

There was also a significant religious aspect to discrimination in the American South. From the period immediately prior to the Civil War forward, religion helped further institutionalize racism in to the social order of the American South. This quote sums it up well. This wasn’t the source I was looking for, but it works:

“In the late 18th century, as evangelical revivalism spread through the region, a brief moment of opportunity for a biracial religious order seemed to present itself. Some ministers declared slavery to be a sin, freed their own slaves, and advocated lifting restrictions on black men who wished to preach the gospel in public. But this moment was illusory. It quickly became evident that whites valued the blossoming of their evangelical institutions and would make the necessary moral accommodations to align southern religious institutions with slave owning. As Virginians and Marylanders had established as early as the 1660s, freedom from the bondage of sin did not equal freedom from human bondage. Despite the presence of the occasional odd anti-slavery southern divine, white southern Christians erected a wall of separation between the realms of spiritual and temporal equality. By the 1830s, especially after Nat Turner’s uprising in 1831, white evangelicals who previously had questioned slavery were defending it as a divinely sanctioned social order. By the 1850s such a view reigned as a virtually unchallenged orthodoxy among white southern evangelicals, be they elite divines or folk exhorters.”

The “divinely sanctioned social order” continued after the Civil War. It was very much an undercurrent of Protestant and evangelical religious teaching in the south. The Klan itself was grounded in part in religious beliefs.