People and organizations involved in the Wisconsin fight

Here's an additional question one of my readers added to Rotherham's list of questions of the people and organizations involved in the Wisconsin fight:

11. Individual Teachers:  Your need for a strong union has long been tied to the fact that local districts have been the sole employer of public school teachers.  Shouldn't you be encouraging a major expansion of charter schools so as to create truly competitive bidding for your services, thereby better separating your fate from the vagaries of politics that the current situation highlights?   Isn't this especially true for the very best teachers who are penalized most by a single-employer system that pays primarily according to time served?