Almost all "contemporary reasonable censorship in functioning liberal democracies" are attempts to prevent people from exploiting the vulnerability of others: speech that causes people to make *patently insane and irrational* medical decisions, for example. Really stupid things like fake cancer cures, and suggestions to drink bleach. And typically, for proponents of censorship, there is a whole spectrum of acceptability as well: the more it's a grey zone, the less the censorship is acceptable. When the censorship clearly and obviously only constrains the actions of malicious actors, and clearly and obviously protects vulnerable people, it's seen as a win. This is always highly contextual, and limited by the extent of scientific knowledge.
A common theme is that censorship to protect those in power (the government) is bad, and censorship to protect those who have the least amount of power is... well, not great (it's definitely always better if it's not needed), but not bad in the same way.
Think about what makes you consider "threatening speech" a "force": presumably it has nothing to do with particle physics... is it perhaps that the act of speech itself causes people to adopt behaviours they wouldn't normally adopt? ie.: that it can carry some coercive weight? That it can be used to exploit/endanger vulnerable people in some circumstances?
Speech may be a very very weak force in most (or even "nearly all", just for the sake of argument) circumstances, but there are tons of examples of speech being a powerful force, causing large social and historical shifts. There are both positive and negative examples of this.