I am opposed to it.

Resolving disputes is what the law is for. Failing that, the ability to deal with those you don't like with without resorting to violence is a basic prerequisite of civilized society.

I certainly don't see why prowess in physical combat has any bearing on the legitimacy of either side in a dispute. Seems mostly like a means for those skilled in combat to take whatever they want from those who are not.

Furthermore, I consider the right to life to be inalienable. Meaning, there is no contract you can enter into to surrender it. Since your opponent in a duel cannot have legitimately waived their right to life, killing them is murder.