Not to say unions can't act petty or spoiled at some points, but that attitude is self-defeating, and the existing counterpowers will stop them soon enough.
Assuming the rest of society is functional, i.e., capitalist. Unions in industries that are enforced monopolies, e.g., government workers, are a problem. For example, here in the United States, teachers' unions are probably the biggest obstacle to fixing the education system.
The idea that education is an enforced government monopoly in the United States Of America of all places makes me question whether you are aware of the importance of private education in that country relative to public education. The idea that a society being functional equals it being capitalist simply makes me question what you mean by capitalism and functionality: try to taboo those words? Finally, the idea that teachers' unions would get in the way of the improvement of public education strikes me as odd and unexpected, and I would like you to develop that point: what do you mean by "fixing" and why are they "obstacles" to it?
I have found this most wonderful (if fairly lengthy) article, and thought you would enjoy having it brought to your attention.
It is so good, I think we should include it among the references in the "Politics is the Mind Killer" wiki page. But, before that, I submit it to you, and ask you: is there anything in this article that would warrant its exclusion from this site? I mean, besides the fact that it is about politics, and written by a notorious Social-democrat (And is that in itself grounds for exclusion?).