There is nothing inherently evil about unions, but in this country unions have evolved to be a very destructive force, especially in Academe. They fight "management" to get as much as they can, and they see it as their obligation to protect the job security of every single union member - especially the worst ones.
One of the major sections in every teachers' contract is the complex and impenetrable procedure for disciplining a teacher who breaks a rule. And every Bargaining Unit has teachers who are incompetent, lazy, and who should have been jettisoned years ago. But ask your local HR representative how many teachers got "unsatisfactory" performance reviews last year (I have, several times), and when you cut through all the bullshit the answer is ZERO.
Instead of complaining about standardized tests being irrelevant, the NEA should be in the forefront of developing tests and other evaluation tools that permit the schools to assess students' progress and explore new initiatives that might achieve some success. But the only initiatives that the NEA is interested in are the ones that mean more money or benefits for teachers (e.g., smaller class sizes).
The school system mirrors our country in many ways. Just as we have an "income gap" that keeps getting bigger and bigger (which I don't see as a problem), we have an education gap, where the kids from the best (generally) suburban public schools can get a fabulous education - equivalent to a good private school, while inner city kids are lucky they can learn the basics because of the classroom behavior problems, teacher apathy, and disengaged parents.
And ironically, money is demonstrably not the answer. Some of the most expensive school districts in the country (e.g., our nation's capital) have the worst educational outcomes, and parochial schools spending well under $10k/kid are kicking ass, as they always have (with non-union teachers making $35k/yr).
But honestly, is there any other factor in this whole picture that has had a more destructive effect than the teachers' unions? I can't think of any.