I'm not an expert, but there are several types of unions. The biggest distinction is public sector vs. private sector. Public sector unions have their own iss

I'm not an expert, but there are several types of unions. The biggest distinction is public sector vs. private sector. Public sector unions have their own issues, but this would be a private sector union. Within private sector unions there are "factory" type unions and skilled worker unions (electricians, plumbers, etc.). In the case where you have a single "factory" in a town, the workers need to bargain together in order for wages/working conditions to not have a race to the bottom. Workers can't take their specific skills learned at the factory across the street and get similar pay since there is only one place to work. For skilled worker unions, the unions allow workers to float through various companies that have work while maintaining their pensions and wages (determined across the entire union hall based on seniority). Companies of course hate being forced to hire more senior workers at higher pay level when their productivity is not that much higher (or even less). A lot of the "bad" reputation with private sector unions likely originated with the corruption associated with the pension funds investing in shady deals. And we all have horror stories about bad teachers protected by the union or "lazy" workers.