The analogy to shouting "fire" isn't appropriate. There is a public interest balance when it comes to speech. The more public the interest, the more liberty you can take with the truth. Falsely shouting "fire" involves no public interest. All it does is harm. But saying the president is a Lizard-person from Mars ... that actually involves something of great public interest; the honesty of a politician. No court will step into that question. No court will trample on someone's right to say any manner of untruths about a politician.

The flip side to this is speech about non-public persons. You can call the president a lizard, but say the same about his kids and you expose yourself to slander liability. False news about non-public persons is already regulated.

Freedom of speech is about the government not locking you up. Private lawsuits are a totally different paradigm.