One man’s modus ponens…

Back in my graduate school days the philosophers among us circulated a maxim:

One man’s modus ponens is another man’s modus tollens.

Amidst the philosophers, I would sometimes make an argument against negative utilitarianism to the effect that if you really believed in it, it would entail that we should make the human species go extinct.  This argument was intended as a reductio ad absurdum of negative utilitarianism.

Two decades on, though, it makes me think that perhaps one man’s modus tollens can be another man’s modus ponens.