You're absolutely right! The two are not the same. Unions are intended to support, protect, and advance the interests of workers. That said, there is one possi

You're absolutely right! The two are not the same. Unions are intended to support, protect, and advance the interests of workers. That said, there is one possible catch. Each union advances the interest of the workers they currently represent as they see them. It is possible that this may not always be the same as the interests of the workers they are advertising to. There are other failure modes, too. A minority union working with one company many sacrifice the interests of their members there in order to gain an advantage with negotiations with a different company. This most famously happened with Hostess, wherein one of the unions that represented a small number of Hostess workers was incredibly hostile in negotiations in order to improve their hand with a different company. You're absolutely right that anti-union propaganda should be distrusted and disregarded out-of-hand. Yet, it's perhaps possible that pro-union interests shouldn't be treated as automatically aligned with those of a given worker or set of workers. As you say, in-principle alignment isn't always the same as in-practice alignment.