Danyal, i know in a big way what you mean!
i was never "racist" until i was hijacked in my driveway, my borther was mugged by 5 guys, and my best friend stabbed in the back, all in the same week. my mother has also been held up at gunpoint, my father has to, i've had a stray bullet(from a shoot out outside my house) nearly kill a guest in my house once, missed his head by inches...came through the window. the list is longer, but that is enough.
after that i became suspicious everytime i saw a car on my block with 4 black guys in it, and i have grown eyes in the back of my head when i'm walking in the street, which is rare because i know it isnt safe.
we have unfortunately been forced to make these differentiations based on our survival instincts. as you said they are instincts and mathematically and logically are perfectly correct. that is because 99.9%(guessing) of these violent crimes are being carried out by people of the black skinned variety.
hearing of people you know dying here because they were shot, suffocated with a pillow while they slept by house thieves etc. is all to common place here.
in fact an unborn baby was shot twice at point blank range the other day in her mothers womb. the baby died, the mother lived:(. South africas youngest gunshot wound fatality i believe. poor thing hadnt even been born.
you also know that the government is being run by black people and that they are doing near nothing to prevent and thwart this violent crime, as well as hiv/aids, and many other problems we have here. they have a genral policy of apathy, but it's matters in which life and death are involved that you expect service delivery!!
it's a doubled edged sword towards being a racist.
this our minister of health addressing the country about it's AIDS "problem". she also accidently made hard drugs such as heroin, cocain, morphine etc legal to possess and use for a period of three weeks once.

fact of the matter is that we are hard hit by crime here, violent crime, murderous orgies of crime that are almost unspeakable. a conservative estimate is that 300 000 people have been murdered here in the past 10 years.

who is commiting the crime? black people mostly. yes they're poor and desperate. but some of these criminals are ruthless killers, you could picture them being dicatators in the postition of men like charles taylor, former leader of liberia.
it's also not uncommon to get vigalante groups who will kill a young 16 year old boy because he stole a cellular phone or something ridiculous, this happens quite frequently in black areas. at the same time because of demographics here, the majority of those being murdered are black people. that i asume, i know they have always had violent crime in their suburbs, gang crime etc.
so the only common denominator regarding the violence here is that it is directed at both whites and blacks alike, maybe their is some racial intention when it is done against whites in some cases.
but yes, it does make you turn hard against black people, not black people in general, but in certain instances where your safety is concerned, it does breed distrust.
as did apartheid breed distrust of whites by blacks. the white politicians here are the brunt of jokes by black people. they dispise them. of course i speak in general.
i judge people based on there actions and as indivisuals, but in some cases you havent got the time to find out and you have to assume A based on B or what not.
a black person that might be getting followed in the street by another black person would make the same judgement i'm sure. you dont expect a whitey to attack you, it's very uncommon.
what has happened in zimbabwe doesnt make matters any better.
conflict breeds racism and racism breeds coonflict. what came first the chicken or the egg? i dont know. it's not a subject i devote much thought to(you woulnt think so judging by the size of my post), if i did i'd never stop thinking about it and would probably land up going around in circles.