The Chicago Strike and the History of American Teachers' Unions - Dana Goldstein

Some people say that public sector unions have outlived their purpose. As Dana Goldstein points out in this post (which she will expand on in an upcoming book), the modern teachers' union movement started in Chicago in 1897 as a response to inequity and unfairness. How does an institution outlive its purpose when its purpose is equity and fairness? Or have ideological forces changed the public's view of fairness? If that's the case, how important are the traditions of the labor movement, and what does that mean for society?