They all invent some rationale for why they are better but all of them are, in the end, the same.
For example, Anonymity plays an outsized role in the equation. FB is as you said essentially the same as Reddit except (most) people self censor to a degree that keeps it mostly cordial. They’re not going to use certain language and allow their full opinions to be heard, because someone they actually know could be reading. (Some people don’t care and post unfiltered but speaking of the majority).
Generally People posting on LinkedIn is often going to be some form of HR speak, they don’t want to offend anyone in their professional network. They’re not going to talk about religion and politics and whatnot.
Mostly I don't. Nearing my 7th decade, I have spent most of my adult life seeking convergence of my private and public self. It's one reason that since the early 90s I have used my initials as my username everywhere.
I highly value privacy but have no need of anonymity, though I understand it's life or death for too many.
And I don't mean I would be the same around a stranger as I am my wife of 35 years. I mean I would be my honest, authentic self for each context. Twitter or nestr, Facebook or Reddit, church or mall, my hometown USA or Berlin.
I rarely comment here because I rarely have any value to add.
I too feel I'm my true authentic self in each scenarios, I'm just calculating risk, disruption, impact to reputation, etc and can always choose silence as a safe option. Although, safe discussion on these topics is often the most interesting to me. It's controversial stuff where my opinions have reason 'to me' but I'm open to hearing other points of view. I don't see my thoughts as immutable so if some stranger on the internet says something I haven't considered, I might just change my way of thinking entirely.
Maybe it's the way comments are weighted here, or the fact that post scores aren't shared, but it's definitely the best place on the web for me.
The non-contributors here here speak in full sentences, cite cherry picked links to back up their assertions of the local dogma and link to the Wikipedia page of whatever trope they want to reference rather than just stating it. These sorts of comments perform the same social utility (tribe signaling basically) to the people who peddle them as saying "yikes" and "the front fell off" on reddit and the snarky bigoted quips they use on the chans. Such non-contributions seem to be of roughly the same prevalence on all platforms, ours are just the most polished.
There's not enough crowd to blend into here. The handles of the people who constantly sling bullshit with shoddy link-spam to back it up, the provocateurs and the asinine ideologues become known and they earn down-votes instead of replies. On a popular reddit sub there's enough people coming and going that there's always someone to take these people's bait.
I think he also found that as two people argued down a thread, their wall of text gets thinner and thinner, and more annoying to read, and hoped that was a deterrence as well.