>>At one point in this country's history, unions served a valuable role, especially in industries where safety was an issue. But the NEA is about one thing: power

You're right, but It's a bit more complicated than that.
Any kind of political or economic monopoly will eventually become decadent and corrupt.
During the industrial revolution and leading up to WWII, large corporations held that kind of power and it was only the government and the unions who could counterbalance that monopolistic power.

Technology and globalization have changed all that and the only surviving monopolies are government entities like school systems, police departments, fire departments, mass transit, some regulated utilities, etc..

We haven't figured out how to counterbalance that power the way we did the power of the corporations and these organizations, as they will, have become increasingly corrupt and decadent.
If you think that the NEA is corrupt and self-serving, try taking on the FOP (Fraternal Order of Police.)
No politician will even think about it.