Who punishes media organizations?
Free speech is a two-way street, and in the Constitution, it relates to government. Elon's talk about free speech is just for ignorant masses since it is his private company and he can decide, and he does, what he will publish and what not.
What happened here is that genius realized two years later that he paid $44bln for a company that was worth, in most optimistic scenarios, $22bln and, in reality, probably $8bln. Most companies don't want their ad being published next to threads glorifying Hitler, and that is why they pulled back, and that is why there were calls for companies to stop publishing ads. Organizations that called out Elon Musk, ALSO have right to free speech! So, he can sue them, but his case has same chances as Space-X populating Mars or Cybertruck being real truck.