Earlier quoted context omitted.
This makes zero sense, you're drawing huge conclusions based on a prisoner's dilemma situation. Of course it's beneficial to be a defector, you get all the benefit but none of the cost. Once no one is unionized at all or it's so small to not have any pull the benefit disappears. It's like saying that taxes are useless because given the choice people would opt-out if they could, ignoring the consequences of if everyon…
How is it a prisoner's dilemma? Why would a union give its benefits to someone who didn't join?
[1] Some unions manage to get payroll benefits for just union workers but it's vanishingly rare because it just pushes workers to the union if they don't give it to everyone.