And simply wearing an orange shirt as a protest are grounds to sack you in the USA. That couldn't happen in the UK because we have freedom of expression.
But it isn't illegal. You can't be arrested for wearing an orange shirt.
I know the incident you are referencing here, and you are completely mischaracterizing it. Florida has some of the lousiest employment law in the USA. It is an
"at will" state, where you can be legally fired without cause, and there are no grounds to appeal against it.
We can trade "my freedom of expression are better than yours" stories as much as folk like but what links that to "another school shooting"?
Either you have freedom of expression or you don't. Suppression of such should be limited to that which is likely to
directly cause physical harm, such as shouting "fire" in a crowded theater, or directly instructing an individual how to build a bomb. It should not extend to saying something that a few snowflakes might find offensive. Justice Oliver Wendell Holmes Jr.'s opinion in the United States Supreme Court case
Schenck v. United States has been twisted a long way beyond its original meaning.
And yes, this does relate to school shootings because its part of the discussion about things that might trigger a student to go on a shooting spree. If you can't see how those are related, there isn't much I can say further that will help.
(ETA: And by the way it wasn't just because he trained the dog to go "Seig Heil" as the judge put it "The centrepiece of your video consists of you repeating the phrase 'Gas the Jews' over and over again" )
Regardless, while that is also offensive, and the act of a scummy individual, the fact is that it was expression which people should be free to make, and if they are not free to make it, then you don't have free speech/freedom of expression - and that it was prosecuted is a not only a farce, it is the action of dictatorships and police states.