I think the best way to approach this subject is to take an objective look at the history of labor unions in the economy and the effects they have had on business. I also think one would have to look at this strictly from a business perspective as I believe the original question had to do with their perceived negative impact on business.

Of course, this may be impossible to answer as an objective analysis may lead to a subjective conclusion. i.e., too many "what ifs" in the equation. This may be why some economists are for them and why some are not.

I think it is safe to say that they have both positive and negative attributes associated with them. While some industries are able to survive quite well with them, one could probably argue that other industries were essentially all but eliminated because of them. I think the merits of the discussion are too broad to arrive at a definitive yea or nay.

I will also add that business ethics (or lack thereof) have necessitated organized labor. The intent of greed in many cases is to fatten the bottom line, but a by-product of that greed is to force a labor force to organize into a union.