But the metaphor does not actually succeed at doing the heavy lifting required to demonstrate that the licence for photoshop falls into the category of "contracts which are unjust and ought be prohibited".

The freedom to make other people slaves creates a paradox because such freedom can not be applied to all humans at the same time. We can not logically be each others slaves, now can we? I find this metaphor (or thought experiment... is this actually a metaphor?) to be very poor personally.