A union is functionally a business which sells labor. It's usually structured so that sales are indirect, with their customers paying the workers directly, but

A union is functionally a business which sells labor. It's usually structured so that sales are indirect, with their customers paying the workers directly, but that's just accounting. There's no fundamental reason that a union should seek to prevent anyone from ever getting fired, anymore than any other business would see to prevent any of their employees from being fired. Likewise, there's no fundamental reason that unions should be bad for the businesses that hire their members. A prosperous client is good for business. Some unions are badly run and hurt themselves. Americans especially tend to assume all unions are this way, partly because of some high-profile examples, partly because of a culture of individualism and association of unions with communism, and partly because of propaganda. But they definitely do not have to be like that.