I think we can be honest and admit that right-to-work laws are a form of union busting because it's a principled form or union busting. And that principle is "the freedom from compulsory association. " After all, that's essentially what mandatory union dues are: compulsory association.
Secular-progressive statists love to invoke the Establishment Clause to herald "freedom from religion," particularly this time of year. So I think we ought to take the same occasion to herald "freedom from compulsory association," because at its core, that's what the Establishment Clause was meant to be: a protection against compulsory association