If you're suggesting that unions prevent abuse of laborers, you might want to read up on labor laws passed in the last century.
Nearly every original purpose of unions, such as child labor, overtime compensation, etc. have all been dealt with by the courts now.
It seems that one of the only purposes of unions anymore is collective bargaining for wages/benefit increases. And I have to ask you... honestly, how do unions make that any better? I'm not in a union and I do pretty good, because if I don't like what one employer pays, I can try somewhere else. It's called competitive forces and it works for employees just as well as businesses.
The labor laws have leveled the playing field in terms of prohibiting certain practices across the board. Name a union lately that has stopped an evil, corrupt business from hiring cute (and dirty) pre-teens from slaving away 14 hours a day for mere pennies? What? The unions don't do that anymore? Hmmm... must be because it's illegal to do so anyway.
I suggest at least finding a better straw-man argument to use when trying to prove how useful unions are.
In construction at least unions peform and employees pay for ALL of the job training.