I worked side-by-side with 2 unions at my last employer. The impression I got was that while most of the folks were normal, the few that constantly used the union to do as little work as possible for the most money as possible gave the entire union a bad appearance, and little was/could be done about the problem children without great difficulty.
One union got tired of it and voted themselves out so they could get better benefits from the company than the union could offer, and then they were all under the company rules, and the problems people were gone within a short while.
We automated the other union's jobs and got rid of them through attrition (retirements and not filling vacant jobs that were no longer needed). At the end, there were 4 guys sitting at a card table 6 out of 8 hours a day because they had nothing to do. That union's shop steward was so pro union, calling anyone that quit the union to work elsewhere in the plant all kinds of names, etc.... but when the company offered her a job outside the union, she jumped on it so fast her shoes smoked. What a hypocrite.
I was fortunate in that half a dozen long time former union guys came over and worked for me and they were real workers. They were all 20+ year older than me, I went to school with some of their children, and I had to teach them how to use the computerized systems that replaced their manual jobs. They loved it, took to it like ducks to water, and really cranked out the production. 6-7 people doing the work of 65 people.
On that note, my mother-in-law is retired from the UAW. At her last job, she was drilling holes under dashboards on military vehicles and mounting the hoods. She made it look easy. Too easy. Some lazy old timer tried to bump her from her position, then couldn't do the work. Then he filed a grievance against the company saying the job required 2 people. The owner of the company and the union reps came down to the line and told him to show them. He attempted and failed and they all nodded their heads. But before they left, the owner asked my mother-in-law to do the job one time. The next truck came down the line, my mother-in-law drilled all the holes, mounted the hood, sat down in a chair next to the owner and drank a can of pop before the next truck came down the line. :laughing:
She lost some union friends that day.

But she was adamant that the guy was just lazy or incompetent or both. Words were had. But the guy gave up and she kept that job for several years until retirement.