From the businesses', employees', and consumers' perspectives, what are the benefits and costs of unionism?

From the text:

But we are warned that "unions have been targeting Wal-Mart for years." Why? For the dues money of course. Think of what you would lose with a union: first; your dues money, which could be $20 a month "and sometimes much more." Second, you would lose "your voice" because the union would insist on doing your talking for you. Finally, you might lose even your wages and benefits because they would all be "at risk on the bargaining table." You have to wonder - and I imagine some of my teenage fellow orientees may be doing so - why such fiends as these union organizers, such outright extortionists, are allowed to roam free in the land.