Imagine for a second that any time you borrowed money to buy something, like a home or a car, you paid that back not by actually paying the loan plus interest, but by a % garnishment of your lifetime wages. That is what equity capital is like.

Obviously, nobody would take that kind of deal. But what if regular loans were just flat out not made available to you? Like, if tomorrow, banks as a class individually decided they would only accept payment in this sort of lifetime wage equity. Then it's not really a choice anymore. One of the options has been taken away from you. If I take a fair deal and have one of the counterparties flat out remove some of the negotiating options - even if they were not the ones taken - is it still a fair deal?

In other words, the argument that fair exchange has been violated is based on the idea that market power can be a form of coercion. If you don't agree, then you can argue that every possible counterparty deciding to only offer you a bad deal is perfectly acceptable and non-coercive. "Natural shorts[0] are not coercion", in other words. But why stop there? I mean, even in outright theft, where I'm holding a literal gun to your head and demanding payment, you could still choose to eat lead. We can redefine theft and coercion down to excuse any behavior we want on libertarian terms. The tautology is not with the argument, it's with fair exchange itself.

[0] As in, "thing you need to exist". You have a natural short position in food, drink, and shelter.