You seem to quite fundamentally, or perhaps simply maliciously, misunderstand your sister? Or maybe I misunderstand you?
- My cat
- The stranger? Maybe
- Because I know how worthless a human being my "worst enemy" is and I could justify the loss of a great many good things if they were removed from existence. If the only "loss" of removing my worst enemy is getting to keep my cat, then obviously, I'll do his family a service and take this monkey's paw.