[stale2002]

The point is here, that even if someone intent is to parody, this can transition into actual defamation depending on the context.

For example, if someone put up a poster, with your name and photo on it, and the poster said "I, the person in the photo, support Killing a bunch of people, on this date, at this time, at this location", this would be defamation.

When you start getting into actual death threats, this can cross the line into illegal defamation.

And no, defamation is not protected by the 1st amendment, nor are many types of death threats.

[CodeWriter23]

Guess we better abundantly optimize for those corner cases until all speech is illegal.

[stale2002]

No, actually. There is no slippery slope that inevitably leads to all speech being illegal.

Instead, the court system in the USA mostly does a pretty good job determining what is or is not speech, and ways of having very limited restricts on speech that only prevent the extremely harmful stuff, while maintaining people's rights.

Addressing these "corner cases" is exactly what the court system does, and it has resulted in a society where the vast vast majority of speech is protected, and only very extreme and damaging edge cases are banned.

[CodeWriter23]

The example posted above fails the "reasonable person" test, which was my point.