Does this question have any practical importance to your life? When Objectivism takes over the culture, are you hoping to be able to challenge your enemies to a duel?
That's a serious query, in a way. Philosophy is for living on earth. Personally, anything else makes me sleepy. Unless answering some philosophic question will serve my life and happiness, I see no point in working to come to an answer. In fact, I'd say that the tendency to contemplate such fantastical questions stems from and promotes rationalism. (I've certainly indulged in that in years past.)
I don't think that's your motivation. I just think you like to pester the philosophers. :-)
So... I have only two thoughts on the matter, and they're as far as I'm willing to go:
(1) If two morons want to attempt to kill each other by voluntary consent, I won't get in the way. I'm not sure whether the government should or not though.
(2) A culture in which slights of honor must be dealt with by dueling is seriously irrational, self-indulgent, and self-destructive. That's the real problem about dueling -- the culture that promotes it, not the government's response.

