Must every venue that invites expressive participation allow all expressions?
No. Freedom of association is a fundamental part of freedom of expression, even if self-imposed limitations are exactly that: Limitations. But the larger and more "general-purpose" a venue is, the greater its ethical responsibility is to avoid interfering, and the more credibility it gains from restraint.
I don't like Twitter's format, so I have no actual dog in this fight. But if Elon Musk intends to turn it into the world's first legit internet town square, I'm glad someone is trying. It's been a very long time since anyone took the idea of the internet as "empowering" seriously, and it's an idea that deserves to be resurrected.
Bigotry is intellectual vandalism, it only serves to smear shit on everything it touches.
There's not one person on this planet uninfected with prejudice. It's normal to be grossed out by extreme cases of it, but thinking we're separate from the problem would be self-delusion. So avoiding it altogether isn't protecting anything, it's just giving the illusion of power to wretched ideas that actually have very little of it.
Not everyone wants to be part of some intellectual root cause analysis of bigotry
It doesn't have to be so cerebral. Sometimes it's just about looking in the mirror, and recognizing in yourself the weaknesses that led others down the wrong path.
They just want to be able to discuss whatever without people taking shots based on who they are. Bigotry and hate speech on social networks literally kills people and there isn't any obligation to keep what was well described as cancer alive.
Lots of social interactions add to the burdens of life and can "literally kill people." It's stressful to see bad things, to be witness to madness or malice, to be betrayed or have illusions shattered. But it's also life-affirming and joyful to see the opposite, and sometimes life-affirming and joyful to even express the positive in the face of the negative.
The people we expect to insulate us from the jaggedness of the world are called family and friends. I don't know why anyone would expect billions of strangers on the internet to do that for them, or why they would think political and cultural debates are supposed to be a bunch of choir-preaching and self-adulation.
Realizing that surprises are possible is the best gift anyone can give themselves.