At the outset, in the late nineteenth century, private unions were needed. Workers needed representation because companies, unchecked and by their nature, took advantage of them. And what a fight that was. Over time, though, private unions became synonymous with corruption and staged their own decline. For my answer I will refer only to public sector unions.
Public sector unions, according to this blog: http://directorblue.blogspot.com/2011/02/brief-ill... didn't appear on the scene until the 1950's. In short, public unions have also become corrupt, but in a different way: they have become tools of the collectivists, the political Left.
The answer to the question would depend, then, on my point of view. If I am Libertarian/individualist leaning, then I would say "no". And my definition of the problems we face in America today would differ greatly from a Social Democratic/collectivist point of view, from which the answer would be "yes".
Personally, I am an individualist. I am perfectly able to think for myself and to make my own decisions regarding my own life. I am unique. I respect myself, therefore I respect those individuals around me as long as they respect me. I take responsibility for my actions. I embrace negative liberty, as opposed to positive liberty (http://plato.stanford.edu/entries/liberty-positive... Therefore, my answer to the question is an enthusiastic "NO".
As tools of the Left, public unions foster two things: social democracy and a money machine for Left leaning politicians. That is, socialism and the financing for it. I am staunchly against that because socialism invariably leads to totalitarianism. Public sector employees are already protected by laws enacted by Congress. So, what are the public unions protecting their members from? Could it be the American public?