The concept of publicly traded companies is multifaceted. In this case the relevant part would be that when you accept the role of a CEO (which I believe Musk is) you take on various levels of liability on part of the investors.

Specifically if a CEO decides to just destroy a company then investor can personally sue him or her.

Overall from what I see the concept of free speech is being misused so much it becomes quite difficult to understand which variant people are referring to.