My attempt at objectivity concerning unions
It's seems like many of the opinions on this board are either pro or anti unions. My take is that it would entirely be based on the time and era that we are talking about. As a general rule, I do feel that unions are outdated in the U.S. and do more harm than good for all of the stakeholders involved, including the workers themselves.
However, it would be foolish to think that unions didn't contribute significantly toward the health and well being of workers (which were most of Americans) during the early to mid part of the 20th century. The idea of children working 6 days a week, 12 hours a days, for a pittance is not an ideal which any society should embrace.
This movie was made in the late 1970s when unions still had a strong presence in America, though they were on the decline. As such, it really isn't out of place and time. I can't comment on whether it was good for this particular factory because I don't know the facts and movies tend to be very biased. However, I wouldn't hold against it the fact that the factory ultimately closed down 20 years later. That is a long time and so much had changed in U.S. manufacturing that the factory would or certainly could have closed down regardless of whether it was unionized or not.
Lastly, the movie was pretty good but nothing great. It wasn't that insightful and it wasn't all that entertaining to me personally.