If the letter wished them a rapid death, would it still be a threat? What if it merely wished them a death of unspecified speed, itself being the natural and ordinary consequence of being alive?
Edit: to be clear, this comment was not asking a serious question
In law, there is a concept of a "True Threat" [1][2]. Political hyperbole is not a true threat; sending a threatening letter whose only purpose is intimidation may be. So Tan's foolish statements are plainly protected speech, and it is sensible for the recipients of the letters to contact police.
I think context matters. I can say "it would be a shame if something happened to you" and that could be pretty clear threat in some contexts and a genuine expression of concern in others. Same for something like "we all die eventually." In the context of a random letter? Yeah just don't, unless you mean to threaten.
It's mentioned in the article that several lawyers were contacted and they all agreed it plainly did not constitute a threat.
> But tying this potential legislation to the message Tan communicated to his 408,000 Twitter followers would appear to be a serious legal challenge: Half a dozen lawyers and judges told Mission Local that, however ill-advised, Tan’s comments do not rise to the legal definition of a death threat.
Which makes sense. Wishing someone a slow death is akin to saying "go to hell." It is a terrible thing to say and can be said with hate and malice and make you feel very worried but it is not the same thing as "I'm going to kill you."
Edit: to be clear, this comment was not asking a serious question