The same way they could think that “closed shop” is right.
Raisin growers are forcibly “unionized” (forced into co-op) and the co-op board has the right to seize dues (raisins) and it is okay because the growers “benefit” from the higher wages (raisin prices) brought about by union negotiation (increased scarcity and raisin promotion).
It is evil, but what would you expect from a FDR program?
being forced into a cooperative sounds like a contradiction in terms