As I said, I think this is a balance of probabilities thing. There are sound arguments either way, and you have elucidated those on one side very well. The counter argument is not one that people unfamiliar with South Africa can really relate to. And it is this:
White South Africans, other than in some parts of the Western Cape, live in constant fear. When you pull up at traffic lights (robots, in SA), you leave a gap to the car in front and have all your doors locked and windows wound up, in the hope that this gives you a split second to avoid being robbed at gun point. This happens constantly. Most white people (and I mean, almost everyone) in SA live behind high walls with glass or razor wire embedded in the top, and have electric gates, sometimes 2 sets. They almost all either have their own private security patrols, or belong to a neighbourhood scheme. They pay armed guards to patrol 24 hours a day. But those security companies aren't beyond a bit of corruption, and have been linked to many violent crimes. Behind those walls, houses all have steel security bars over the windows and doors, and many have internal safe areas in which to retreat in the very real chance that armed robbers or kidnappers enter the house. Every single white South African knows of someone who has had been injured or killed by house breakers or car jackers.
This is a deeply broken society. The police are corrupt and incompetent, and the inhabitants of the slums alongside the affluent areas have nothing much to lose in this wave of criminality directed against their former oppressors. There are clearances of white farmers going on in South Africa at the moment at much the same rate as happened under Mugabe in Zimbabwe. A Justice Minister in a recent government said something along the lines of "what's with all this moaning about crime?" Many white people see the whole environment as one of settling old scores with official connivance. One of the results of all this is a mass exodus of white South Africans to the UK, Australia, New Zealand and so on.
Osacr Pretorius wasn't an outlier in terms of his attitude. He is actually typical, and, sad as it is to say it, he was understandably typical. South Africa is in deep trouble, and the whites of SA feel like they under siege. So, live with all that your entire life, and then hear a noise in your bathroom in the middle of the night..........