Maybe it's always positive for poor performers since they become entrenched, but not always for workers generally, and not in the larger picture.

If you don't think that's true, then why not start a company where you build in a union from the start? You can even have all workers be owners with equal voting rights. There's nothing stopping you from doing that! Or join an existing one, as they exist, even in the US. It's completely legal and you won't be opposed.

Forcing your model on existing companies is where it becomes objectionable. Start your own if you think it's a better approach. If it is, it'll win out and you won't have to force it on others. They will copy it willingly and eagerly.