Of course the norm would be "don't reply to words with violence",

Note that arguments are different to words.

With respect to the more general norm of responding to words we already inherit that norm via the laws of most countries where we reside. In those countries where such a norm is not enforced following the norm is quite possibly a bad idea. There are (and even more so have been) places where violence is an acceptable and even necessary response to certain types of words. This perhaps even applies in certain subcultures within the more developed countries. I don't have a problem with that - it is their culture, not mine.

Because we don't have the ability to punch each other in the face over the internet and only meet in person in the location where we physically exist it is the norms of that location that are relevant. Such a norm does not belong here.