Good opening effort Iain, and I've seen your posts, you're one of the people I thought of who puts work into them!
One of my amusing mini hobbies is to make semi-scientific charts and diagrams of stuff. There's one going on here. Consider a Tree diagram - either vertically or horozontally is fine - that starts out with The Communication Medium Subset Content Guidelines. Here, the Communication Medium is all of DC, but this analysis applies to basically anything, from public parks to malls.
Branch #1: Governmental vs Corporate
This means that "Free Speech" works profoundly differently in Government controlled Public Areas vs Company controlled venues. Not counting sleaziness, playing it straight up, Free Speech is all that stuff you learned in 5th grade. Say what you want, don't call Fire in a movie theater, no slander/libel/harmful intent/etc. Otherwise - THEORETICALLY - you can say what you want.
All the rules change in Company controlled. (Even if Mouser doesn't have a Biz name, it's still his ballpark, basically still Company controlled, such as a sole proprietorship.) Then it's all TOS/Code of Conduct/etc. Put fairly simply, there is more censorship on all Company controlled venues. How much then goes into the branches below.
Branch #2: "Acceptible vs Not Acceptible".
I basically disposed of this for the Government areas above. For Company controlled areas, it's all about the Company's vision of what they are offering. This ranges all the way from zero monitored areas that can indeed include a bad trolling culture, yet even that is at the edges of the entire concept of speech. There are some ways to handle that, but nothing's perfect.
There's various ranges of light-medium moderation, with 1000 different styles. You get a medium-good environment.
Then there are tightly controlled environments doing the whole "Family Friendly thing Safe For Kids". AOL used to be famous for that, Facebook might be today.