Here's the thing. . you can't paint with a broad brush on organized labor in general. There's been alot of good done by unions. There's also alot of abuses.
Without condemning all unions. . .because I like some of them. . . The teacher's union is pretty much a mess. There are many studies and articles to back this up. Here's one. There is history to back this up. I have personal experience to back this up. My mother is a career teacher who has never joined the union in 20 + years. She's one of the best teachers in her district, and has always done an amazing job.
So, let's be a little nuanced on this whole Wisconsin/unions issue. I'll just put in my 2 cents and say the teachers union could use some wholesale reform. . .or dissolution.