Why Do Many People on the Left Oppose Any Union

Why do many people on the left oppose any union participation in joint ventures with management?

A) Workers don't like the joint ventures.
B) Union members who take part in such ventures are forced to study things like economics,finance,and accounting.
C) The ventures never work.
D) The ventures are too costly.
E) In their view,participation amounts to a conflict of interest for unions,whose job it is to represent workers rather than co- manage enterprises.