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.