JerryS
I think there is more than one thing going on here, some more pernicious than others. For example, the comment about being “useless to any black man” speaks volumes of nasty stuff, both racist and sexist, because it implies at the very least that you are only “useful” as an object of a black man’s attentions. Somewhat less vile is the general and apparently inherent tendency for groups of people to sort themselves out by drawing boundaries, and at various times and places to enforce those boundaries to different degrees. Although many minority groups view this as defending themselves from being swallowed up by the majority, being a minority group doesn’t cause this behavior: Often a majority group resists what it sees as “contamination” by minorities. The root seems to be a drive to preserve “us” at the expense, if necessary, of “them.” We can all think of examples far less striking than skin color, wars of extermination being fought between two groups that are indistinguishable to outsiders. I suspect that this is least in evidence when the majority feels secure; I think that security leads to tolerance. This tolerance can easily evaporate if the majority suddenly feels threatened, as happened in Germany between the wars and in the Arab countries after World War II.