Steeling ourselves to act in solidarity with someone like Christine O'Donnell is a useful exercise because patriarchy is often exercised by popular and influential persons within a group. While the victims of patriarchy aren't necessarily unpopular, exposing such behavior puts their reputation at risk. It can make them unpopular very quickly, as when the perpetrator enjoys good standing within the group, or is dominant by some social criteria.
We do well to recognize this as a likely scenario in which patriarchy will impact our lives. It implies that standing up for someone who deserves it is very often a decision that carries a real social cost, and will not be universally praised or rewarded amongst those who are otherwise like-minded.