Why are you afraid of people? Because people are scary! That's why!
Personally, my fear of people stems more from the possibility of negative judgement rather than potential cruelty/harm. I'm not afraid of people pulling a gun on me or trying to hurt/embarrass me. I don't think anybody's out to get me. However, I am extremely fearful of people thinking I'm stupid or boring or incompetent or ugly. I suppose it's silly to give people's opinions of me so much weight. But I can't help but view it as a reflection of my self worth.
Now that I think about it, I suppose it's kind of strange that I don't see that many threads about the fear of being deliberately hurt and taken advantage of. (Maybe I just don't notice them because I can't relate as well.) I wonder if that can be classified as a type of Social Anxiety Disorder or if it's a completely different anxiety disorder.