"Eventually you build no karma," sayeth the soothsayer. The implication of that questionable sentence is that's when the discarded outcast is finally destroyed (or destroys him/herself) for the sake of the community. She serves a vital purpose, to draw the ire and inchoate hatreds of the group upon herself. This is seen starkly in the short story, "The Lottery", by Shirley Jackson, which depicts a wholesome farming town (I believe it's in the northeast), that depends on the community to gather together for the ritual of harvest day.
It's tantamount to sexual hysteria and can be whipped up in several ways. We saw this occur during the McCarthy era, when Joseph McCarthy, Senator from Wisconsin, seized upon the idea of Communists lurking among the American population, stoking the notions that ordinary citizens were infiltrating society in order to bring it down. The fear that spread like a virus through the country tore apart lives but helped put notches on the belt of Roy Cohn and Richard Nixon, who later became President. It also occurred in Salem, Massachusetts, when accusations of witchcraft ended the lives of several women. The hysteria whipped up serves several functions: bind the group against a common enemy and project internal hostility and rage upon an outsider.
Unfortunately, it is probably difficult to actually be the outsider, the target on whose destruction the group depends. There are many methods utilized against the target: threats, attempts to discredit, or even driving her to the brink of sanity. On a continuous basis, day in and day out, the perpetrator cannot help but succeed, particularly if the group does not step in for fear of becoming tainted themselves.