Make it so people can say whatever they want, but it's easy to decide what level of discourse you're personally willing to listen to. You have the right to say what you want and other people have the right not to listen.
It's not an easy system to develop and maintain, but Twitter pays well enough to afford people who can do it. The goal just needs to be set.
i think a big problem is monetization. You have to identify the conversations with the most participants in order to get ads there for sales. You have to design feed algorithms and promote certain users to drive views and adclicks in order to sell more ads.
If Twitter goes private then maybe the income expectations change and therefore the platform algorithms can change. I don't use twitter but it seems like putting more moderation power in user's hands ( chronological feeds, easier management of what you see and what you don't, etc ) becomes possible when Wall St. expectations are no longer a part of the design process.
If you don't have a stock price to answer to then you can do things that create a healthier community but may not be the most profitable.
EDIT: You know, Musk be on to something about leaving a company private. Tesla is public and the shorters almost killed it, he really had to fight them and still does. SpaceX was left as private and is thriving. maybe he's taking lessons learned from both Tesla and SpaceX and trying to apply them to Twitter? just a guess
It's not an easy system to develop and maintain, but Twitter pays well enough to afford people who can do it. The goal just needs to be set.