My argument isn't we shouldn't do it because it's hard and messy, it's that we shouldn't do it because it irrevocably harms the community and society so the community and society has a right to try and stop it.
It does serve people, if that father fails the suicide attempt or gets busted by the cops before he can duel, then we can put him in treatment and try and help him out which can keep him alive and supporting his family. If we just throw our hands up and say "you do you" and he gets himself killed for sure then there's no helping him or his family.
Your seems like an argument against having laws against anything then. Yeah people are going to do crimes, that doesn't mean we as a society shouldn't try and dissuade them from doing it.
If you go by this logic why shouldn't we have ash trays in bars? Sure we as a society think smoking in bars is a nuisance, but some people are going to do it any way so why make it messier and more complicated for them? Should we not even have laws in place banning smoking indoors?
Laws and rules also have a normative function as well. An indoor smoking ban isn't really enforced by the state, and not even by the bartender as much, it's enforced by everyone at the bar who understands it's a nuisance and will yell at you if you do it. We as a society shame those who break the rules, and we should be shaming people who do extremely selfish acts like suicide or dueling. If it were allowed and normal more people would engage in these acts as there's less of a cost to them.
