Two of the most damaging misconceptions people have about labor unions are (1) that union members tend to be substandard workers (lazy, unreliable, surly, privileged), and (2) that union members can't be fired because their "masters" will always go to bat to protect them.
Where they got the notion that union members are incompetent employees is a mystery. After all, even a cursory analysis of the economics should make it clear that union jobs—those, typically, with the highest wages, superior benefits and best and safest working conditions—are going to attract the most talented workers in a community. Why wouldn't they? Why wouldn't the best jobs in a community attract the best people? Yet, we allow ourselves to be swayed by the propaganda.
And as widespread as this anti-union propaganda is, it's especially virulent when it comes to public service unions. Apparently, everyone and his brother (including President Obama and his Secretary of Education, the corporate lackey Arne Duncan) just naturally assume that it's the teachers' union that prevents conscientious, well-meaning school administrators from firing bad teachers.
People like to believe that if those grossly incompetent teachers did not belong to a powerful union, if they did not have cadres of union lawyers standing by ready to defend them, the administrators would be able to drain the swamp, to rid our schools of those union-created monsters who are holding our students hostage, depriving them of a decent education. That may be a gripping narrative, but it's total fiction.