I read your post again ygolo, and it is really well put. I also understand the role of perception and why it's relevant. If someone happens to be confronted with some particular negative trait, it makes sense for them to have heightened awareness and distrust of that trait. Whatever aspects of their environment produced the initial problems are likely to reproduce the same scenarios. In one way prejudices help people filter down threats to those they are most likely to encounter. This probably is more effective when one's environment remains small and consistent. It's when prejudice is applied in a more universal context that it creates bigger problems than it originally attempted to solve.