The most obvious thing at first: I AM A GERMAN!
No, I'm not a blonde! I don't wear a mustache! I don't like to wear brown uniforms with a read band around my upper arm! But, I do have blue eyes and I am a great brute, really, because I would prefer Germany to be much, much, much more greater, that our eastern border, the natural eastern border, should be the Weichsel. Ok?! And what ist much worse, my english is not good enough, not good enough to your expectations, and not good enough to my expectations. And everywhere in the anglosphere, you would regognize my as a german, because you have prejudices, who seem to be true, like most prejudices!
The sense of prejudices is, to make life a little bit easier. If you have a set of prejudices, well founded prejudices, you prevent lots of harm. It is the hard way to learn, that in the wilderness a lion is a dangerous animal, when your head is in his mouth. And it is very wise to accept, that a lion is a lion and not a social construct. Our brain is able to categorize the world, to separate dead and living things, and to form groups of things and events, which are quite equal and to assign characteristics to each seperate group, properties, to handle them. The name of the game is objectification!
Objectification cuts all, what is individual or special and leaves a model, with all qualities, that are common.
When you see a stange woman, who looks like sluts do, who behaves like a slut, the chance is high, that she is a slut. And if you want to form a longterm relationship with a decent wife, it would be bad advice, to try to form this relationship with such a woman.
The same is true for men. If you find a dangerous man, with a long chain of changing relationships, with that sort of lifestyle with the big ME above, it is not wise, to choose this man, if you want to form a happy familiy, with a caring and sustaining father, a real good dad.
Every group of immigrants to the USA had their problems: the englishmen, the german, the italian, the ires, ... And all groups of immigrants made it. But one group did not: the blacks.
Yes, there are exceptions. There is such a thing, as white trash. Not every asian immigrant excels in math. Not every german immigrant is hardworking. But over the time you will find the bottom of society flooded with black people. And there is no country in black africa, which excels. And don´t mention white colonialism.
This is not a question of worth. We all are born equal (of equal worth and dignity). But we are very, very different and not only by culture. And so it is, that the black community offers a lot of excellent sportsmen, but, in relation to the germans or the jews, very little intellectuals. And this fact is obvious and a well founded reason for prejuctices and everyone is able to recognize a negroe, when he sees one.
Or take as example the arabs. In the arabian world very few scientific publications and more general, very few publications at all are to be found. And this is true for the whole muslim world. Why are muslims, in relation to the western wold, so dumb? Nature or nurture? Probably both! And they replace these lack of excellence by vociferation, religious zeal and violence. The results are to be seen and are the source of prejudices.
The time, when you needed dumb, strong men to fullfill a task, is long over. And so, living in a modern society, I'm not happy if there is immigration of black people or muslims. Yes, there are prejudices, but they are well founded. I'm not inclined, to take risks for my country and my family, only to overcome these prejudices.