This is one of those issues that almost amuses me with its idiocy, until I realize I fall on the sides of idiots.
If two people want to sign documentation to say the other one has permission to take the other one's life and vice-versa, what should I do about it? If someone who is mentally stable (perhaps a stretch under the circumstances, but go with me here) would not mind losing their life in the pursuit of fighting someone else, why should I care?
This is, I would hope, not an issue that comes up very often. And if legal, it should at least require a legal agreement beforehand. If someone just says "he challenged me to a death match on the spot, I swear!", I do not think that constitutes sufficient reasonable doubt.
This is one of the issues that I do not care about, in all honesty, but if it came down to it, I'd have to vote to legalize them.
I could see a defense attorney saying something like: My client did not know that you had to sign this documentation for a death match to be legal! He is clearly the victim of our bureaucracy. The specifcations for duels should be made clearer or abolished.
Then if the dfendant is declared guilty it will open up another "serious" like ones about the death penalty. Many will argue that he was just an innocent man who was challenged to a duel.