The argument is understandable - if you're not forced to join the union and pay for it, then everyone will just not join and let the union still negotiate on their behalf; and it'll have no money to operate and fall apart.
However, I'm sure there would be other ways (for example, if the union is negotiating with the company, the company can just pay for the union, it does indirectly through salary anyway).
However, I'm sure there would be other ways (for example, if the union is negotiating with the company, the company can just pay for the union, it does indirectly through salary anyway).