Try this. Look at your pay rates and work rules that your union negotiated and compare that to the amount of union dues taken out of your paycheck. Next, ask yourself if that is money well spent.
Each management/union relationship is unique and I don't think one can definitively give a yea or nay answer to whether unions are good, bad, or indifferent.
For example, I am happy with the services provided my independent union. On the contrary, I would not want to spend a single dime on ALPA representation.