if you modify the scenario a little bit and add a second attacker the need for disabling one of the attackers becomes more apparent...perhaps killing goes to far, but that is only the logical extension...
perhaps we should ask "Should we break an arm to stop an attack, or dance around, get cut and hope for reflection and redirection?"
Like someone said above...it comes down to instinct. It would be nice to believe that we could stop and talk to our attackers, offer them some tea and have a chat and go our separate ways. Unfortunatley, in the street the attacker(s) are less concerned with manners and more concerned with hurting you.