system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are labor unions viewed negatively and what are their biggest problems?

Everyone I've asked has always had a very negative opinion on labor unions but they have never really been able to give me a good reason why.
gpt
Unions often suffer from the same problem that most large organizations tend to have. After a while, the organization efforts drift from whatever their original goals were, and instead start to focus on justifying and prolonging their own existence.

Say a bunch of workers have valid demands about workplace safety, or salaries, or whatever, and so they start a union. After a few years, a small strike or two, and a lot of negotiation, the union helps win some raises as well as significant changes that make the workplace much safer. So what happens next? The union probably isn't going to disband. The union heads probably aren't going to just give up their jobs. So the union has to find new things to fight for to make itself seem relevant enough that the employees will keep paying union dues. 

But there's not really any strong, valid worker complaints left. So the union starts raising a stink about things that aren't that important or valid. They might demand continued salary increases beyond what the company can realistically provide. They start defending anyone who gets fired, even if they honestly deserve to lose their job. They start to reflexively oppose any sort of change within the business, even if those changes are in response to real and significant changes in the marketplace. They can sometimes destroy a company's ability to effectively compete.

It's a lot like politicians, in that union leadership can often end up doing things because they think it will help them keep their position, rather than doing things because they're the best thing to do for the employees. And of course, especially in bigger unions, there's a lot of money involved in the system, so it's often ripe for corruption.