Note that Facebook and many other social media sites go out of their way to prevent the same person having two accounts. It is against their terms of service, and they do try to enforce it in various ways.
In your example the problem was that someone's mom was reading all of their posts and not that they wanted to use different login information for each profile.
Still, the comment above used both profile and account to refer to the same thing ("create a new profile", "your hobby account") so I'm not even sure which they were suggesting.
A "baseline" where, as mentioned above, misogynistic, racist behaviour isn't allowed sounds easy. But is it though? You take what Nazis and racists have said for ages and put "Russian" instead of their victim of choice and suddenly most Americans will agree that's fine behaviour "because Ukraine".
How about age limits, alcohol, sex? Hell, even Americans couldn't agree on a baseline in those.
I don't know if you're American but as I said I'm not and the internet has teached me how to behave as one online to not be caught in strange Americanised moderation rules. That's not agreement but enforcement that's caused this and if asked I would vote No to those rules.
I doubt you could get just American communities to agree.
Large social media sites are a pale shadow of an actual community. These sites love to throw that word around to get you to sign up, then act like properly moderating their sites to actually feel like a community is impossible.
This is solved by people just make another profile to keep it separate. It is okay not to add your mother on your hobby account.
>These are two different communities that most certainly cannot be welded into a single forum.
But sites like Facebook are not just a single forum. Each group can be it's own community. People can keep two discussions separate.