The post asked for an example of someone who had murderous intent (prejudice), who would turn on someone close who was found to have tainted blood. Her murdering her bro was based on political aspirations, not a need to purge the world of some 'taint' that she discovered her brother had become infected with.
In terms of plotting or being 'nefarious', women may have an edge, on the average, as they usually have to be 'sneaky' in order to overcome the male's advantage of muscular strength. However, among the pinnacles of nefarious, cannot be ignored the writings of Machiavelli -- while women might average higher in some area, males almost always have a greater std. deviation, and can produce single examples that are likely to exceed the best female (with the converse also being true -- i.e. chances of producing the greatest idiots).
