Black Men and Public Space

Black Men and Public Space is an essay by Brent Staples about him realizing and understanding his own ability to alter public space in "ugly ways." The stereotypes of black men give many people, black and white, the impression that black men are dangerous. The act of a white woman clenching her purse while in the presence of a black man is not new. This action happens a countless amount of times a day, but why? I don't understand why black men are the only men that are stereotyped as bad or dangerous? There are plenty of white men that commit the same crimes that black men are stereotyped as commiting.