I've heard widely varying things about different individual unions. But I think this is true of any power structure: whenever power is acquired, it can be abuse

I've heard widely varying things about different individual unions. But I think this is true of any power structure: whenever power is acquired, it can be abused by the few - be they politicians or CEOs or union leaders - or it can be held onto by the many and used for the general improvement of circumstances. There's always the risk of corruption. But speaking very broadly, the higher the number of different powerful parties competing with each other, the better. In literal terms: I'd tend to think having union fat cats arguing with corporate fat cats is better than having only corporate fat cats, who are free to do whatever they please.