I agree, monopolies are not good for anybody with the exception a few people.
Unfortunately, corruption is not confined to unions. It seems to be a human affliction, and as such, can be found in any human endeavor - even at high levels within the church.
The difference is that no one suggests we do away with churches because some leaders and members are corrupt, or that we do away with corporations because some are corrupt. We tell eachother the abuse is the exception and that the intuitions, themselves, are basically sound - why not with unions?
IMHO, more than any single issue, the last election was about people deciding that monopoly of the House, the Senate, and the Whitehouse by one party was a bad idea and that our interests are better, if imperfectly, served when a variety of interests are represented and no one person, party, organization, institution, or economic interest has a monopoly.