Well unions are pretty useless right now for the average American worker precisely because they're so weak, so to many of us giving them money sounds exactly like economic exploitation. Moreover the benefits of union membership are based on seniority meaning that many union advocates have a vested interest in seeing the union expand... but for new members the benefits aren't so great. Tbh it can sound a bit like paying into social security when you're not the one receiving the checks.

At least, those have been my more negative thoughts on the topic. I get that unions used to do some good for workers but it mostly seems like they're in it for themselves and I don't see the benefit to the average person.

Sort of a chicken-and-egg situation, I guess. If you're a union I don't want to pay you for nothing--and you can't do anything for me if I (and a ton of others) don't pay you. I'm not an expert at all on this, this is just my limited personal perspective.