To better understand antipathy towards unions in the US, do a google search for "new york rubber room". Tens of millions of dollars a year spent on salaries for teachers who had to be pulled from classrooms but couldn't be fired. Due to the backlog of arbiters, they sit around doing nothing at all. It's bad for them, bad for the schools, and bad for the public.
It's an extreme example, to be sure, but it is also one that had gotten a fair amount of media attention. No-one wants to work hard when they see someone else taking it easy, knowing that their next pay raise is more closely tied to seniority than it is to on the job performance.
Another example is the number of states where unions arranged "votes" to force "home health care workers" to unionize. That is, if you are taking care of a family member who recieves certain kinds of disability welfare, you are automatically deemed a union member, and the dues are taken from the welfare payments.
It was nothing more than a blatant money grab when it happened where I lived, and I can assure you that these peope got far less from their "representation" than they got in dues, since they were never technically employees in the first place and no bargaining or contact to begin with.
Yes, there are better ways that unions can operate. There are some good unions out there. There is also plenty to criticise too, and pretending that they are a universal good isn't helping anyone.
Edit: perhaps the biggest complaint is that the unions are too powerful. Even leaving is hard; the New Haven firefighters had to file a lawsuit to stop the former parent union fron sending their members to collections agencies for their dues after they left. https://www.nhregister.com/news/article/New-Haven-firefighte...