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.

You lose your freedom of speech when you willingly sign it away in exchange for power and responsibility.