Conservatives would like to blow them up and prevent them from ever forming.
OThers find the labor movement a crucial component of the political process.
There are spectrums to every perspective. Unions can protect the interest of the workers when they are being mistreated. They also can be a bunch of goons.
Interesting article here: http://www.salon.com/news/the_labor_movement/?story=/politics/war_room/2011/02/25/dimick_lind_unions
Collective bargaining is one of the most crucial roles of the union. Without it workers are generally exploited by profit maximizing firms (yes I know this is a wild generalization). But to wipe them off the face of the earth like Republicans are trying to do in Wisconsin, well, I don't think that's our best option either.