For instance,Canon law in Germany attached ecclesiastical penalties to dueling. The reason why was that, although dueling was already prohibited under German secular law, thi prohibition was rarely enforced, and at some of the German Universities, dueling (sometimes with sabers!) was rather an acceptable thing for a young man to do, in particular in defense of his "honor." Having a saber scar across one's cheek was romantic and "distinguished."
So the German Church specifically penalized it, not because dueling is worse than other kinds of fighting, but because secular society was way too accepting of it.
Thanks, that’s very informative. American society was very tolerant of duelling around the turn of the 19th century, but perhaps the Church wasn’t sufficiently influential to even bother bringing it up.