Problem with your whole post is right there. Most all school administrators are former NEA member teachers. They liberalized ZT.
Teachers Union Facts
First off, we're talking specifically about ZT now. I didn't see anything on that site that talked about teachers union support for ZT. I don't deny that there are some teachers (or their union leaders) who are for ZT, but for the most part those groups are NOT FOR ZT, especially in it's current form.
I also don't get the statement "They liberalized ZT". What does it mean to you to "liberalize" something? I know the answer, but do you?
If you're going to try to justify the claim that liberals are for ZT at least make the link you post pertain to that topic (you know...like I did).
If you want to open this thread up to the discussion of unions in general (including teachers unions) we can do that. I'll leave that to you to decide.