That assumption was not at all obvious, if you want to talk about imagining facts.

To address the argument, it's not fair to assume that recipients of such threats would be either willing or physically able to respond. People with kids will not go around dueling people in the modern era. In my opinion, it's nothing more than a fantasy world. We have a justice system and law enforcement officers. Maybe they don't do a great job, but it should in no way fall to the individual, no matter how zealous they may be.

I'm not suggesting that it should fall to the individual, but that the individual have some latitude to defend themselves against a credible threat rather than being expected to just put up with it and hope for the best.

as much as I like the idea, I think it is a fair point to make. the original context for this discussion was threats made over the internet. it is actually kind of hard for a normal person to authenticate the identity of someone over the internet to a degree of confidence that justifies a killing in self defense.

The bulk of personal threats and violence takes place between people who know each other and is not so difficult to authenticate; likewise there are many ways and people willing to help identify the authors of internet threats.

The point again is not so much that 'this will solve the problem' as 'threatening people should have a significant cost' and this is one way of significantly increasing that cost without needing to appeal to state actors whose alacrity and integrity may be open to question.

This approach maximizes free speech while providing the targets of objectionable or harassing speech more options for responding to it.