Re: Would you kill an attacker?
Firstly, it is highly overratd they idea that you could do so - it is more realistic and fighting oriented thinking that _you_ could be killed, for it means you entertain no romantic idea about fighting (romantic being: I show up and being so aikifabulous i beat him/her off like a nuisance...) but that you realize fighting is inherently dangerous. In this regard, being killed is not a function of the ability of your opponent, but precisely of his reckless lack of experience.
An experienced fighter is not exprienced inasmuch as s/he knows how to kill you (any idiot with a gun knows) but inasmuch as s/he knows how not to do it.
Consequently, i would never kill an attacker because doing so would prove that I am no martial artist but just another street thug.
However, I might break an arm - this only in case the adversary proved so dangerous to me that incapacitating him/her seems necessary (ie: s/he extracted and knife and randomly tried to slash or stab me, regardless of how or where).