I think one can make the argument that, in all of those cases, the speech is not the thing being outlawed. A threat of aggressive violence is a statement of in

I think one can make the argument that, in all of those cases, the speech is not the thing being outlawed. A threat of aggressive violence is a statement of intent to commit a crime. You're punished not for speaking what's on your mind, but for planning to commit a crime. (And I specified aggressive violence because self-defense is not a crime, and I think that stating "I intend to defend myself with violence to the extent permitted by law" isn't a crime either.) A scam is also a statement of intent to carry out a crime—fraud, specifically. With spambots, and also with what I'm guessing "abuse" refers to, it's more like harassment or stalking. You want to be able to say "I should be able to walk through this space without being constantly followed by people who are deliberately doing so and ignoring my requests to stop." That depends on exactly what "this space" is—if you own the space, then of course it's up to you, if your harassers own the space, then of course it's up to them, and if it's some "public" space, then it's not totally clear if it's owned by no one or by everyone or by the government, but at least in the latter two cases, it seems reasonable for "everyone" or the government to have rules against harassment and stalking (and I'm saying spam is low-level harassment). Facebook seems to be attempting to act like a "public space" in this regard, though not in all regards.