In the 1920's and 1930's, unions made a lot of sense. Big companies exploited their workers shamelessly, and only by organizing could workers get enough leverage to improve their pay and working conditions. Unfortunately, many unions eventually evolved past their original necessary functions, and became power centers for their leaders (and sometimes for the mobs). The result was unions whose incessant demands eventually brought down the very companies who provided the jobs in the first place. In industries like the steel industry, union wage demands eventually drove most of the steel business out of the country. In the auto industry it bankrupted the companies, who would have disappeared entirely by now were it not for a government bailout.
The July 24, 2010, Washington Post article Rhee dismisses 241 D.C. teachers; union vows to contest firings, is yet another example of how unions are now part of the problem, not part of the solution. All across the country, teachers unions oppose any steps to tie pay and jobs to performance. In almost any other industry it is taken for granted as a fact of life that poor job performance will lead to being fired. Not with union teachers, though.
We have serious problems with our national education system, especially at the elementary and secondary level. Things aren't going to get better until we make changes. Teacher's unions are almost unanimously against almost all the changes that are needed - dropping the seniority system, pay for performance, requiring better teacher training, standardized progress testing, etc. etc. It is yet another example of how unions have ceased to be a help and become a problem themselves.