Earlier quoted context omitted.
> "At our company, a number of job functions are union-only work, meaning it is a violation of the union contract for any non-union employee to perform that work." That's not a union, that's a guild. A medieval-style guild has a monopoly on a certain type of work. A union merely represents its members in workplace negotiations.
That might be your definition, but unions do this also. Maybe it's different in different places - but here the union clearly forbids non-union workers from doing various types of work.
Because the argument "the wrong way is the only right way" makes no sense. If it's wrong, you fix it. Being forced to choose between two wrongs is no good.