The difference I see between Twitter bots and the other classical examples you mentioned is that anyone and their grandmother can make a destructive Twitter bot

The difference I see between Twitter bots and the other classical examples you mentioned is that anyone and their grandmother can make a destructive Twitter bot on a given day, with comparably little effort, negligible expenses, high anonymity, and hardly any traceability. Which I mean is basically the foundation of Twitter: it's based on the premise that everyone's speech should have worldwide reach with absolutely minimal effort. Whether the larger picture is a good thing or a bad thing, it does mean the bot problem is very much a novel problem and you can't just pretend is similar to the classical ones and deal with it the same way.