So is a threat to the President a freedom of speech issue? It was just speech. How about if you use such speech to manipulate the market? Or slander? Libel? Obscenity? Telling someone to kill themselves (spoiler alert: you may get convicted for involuntary manslaughter)? [0]
In this case the fine was not for the speech but for the market manipulation. Saying "oh we were the victims of a hoax and just believed what a random site said" is not a defense. Case law obviously has plenty of precedent for consequences of free speech.
Yes the 1st amendment guarantees freedom of speech and this is where all the confusion starts. Everybody has their own definition of freedom of speech. Most are wrong or uninformed [1]. Given that even the Supreme Court has varying opinions on this from time to time just says it's not an easy topic. No, you don't have a blank cheque for saying anything you want without consequences. Speech is still very much regulated, written press and broadcasting are regulated (differently), etc. You have laws that criminalize slander, market manipulation, etc.
Your freedom ends where another person's freedom begins.
> So is a threat to the President a freedom of speech issue? It was just speech. [...] Or slander? Libel?
As I said, the exceptions to freedom of speech are extremely narrowly carved out. What you're discussing is incitement to violence. There is a very high bar to prove incitement, libel or slander. It's almost impossible to libel a public figure, for example. Almost anything you could say about a politician is considered protected political speech.
> How about if you use such speech to manipulate the market? [...] Obscenity?
These are restrictions that apply in very specific circumstances (e.g., representatives of public companies, television/radio hosts on certain regulated spectrum).
> Speech is still very much regulated
In extremely narrowly defined circumstances, which usually have a very high bar of proof. The general trend that I have observed since Trump's election, which I find very worrying, is for many American liberals to begin calling for greater regulation of speech. The 1st Amendment is incredibly expansive, which is one of the most appealing aspects of the American Constitution, in my opinion. In other countries (e.g., the UK and Germany), it is much easier for the government to regulate speech, which I don't think is healthy for democracy. It is easily for those in power to abuse such restrictions on speech.
If your speech negatively impacts another citizen, and your speech turned out to be all lies, you are absolutely liable for the consequences of it. The "government" is simply here to handle the arbitration.
Only under very specific and difficult-to-prove circumstances. These exceptions to freedom of speech are very narrowly carved out, and for good reason. The broader the exception, the easier it is to instrumentalize for political repression - and there will be a huge desire to do so.
Freedom of speech does indeed mean freedom from consequences for your speech - at least governmental consequences.