First Amendment, normal form:
I do not agree with what you have to say, but I’ll defend to the death your right to say it.
First Amendment, extended to defend Nazis:
I do not agree with your plans to murder me and my family, but I’ll defend to the death your right to make those plans.
Not all Nazis pull the trigger personally, but they are organized around the central idea that this is the endgame. In law, that’s called criminal conspiracy, and even the people who don’t pull the trigger are culpable.