As for free speech in public spaces as restricted by the government, the standard comes down to imminent risk of harm. You're not allowed to scream "Fire!" in a public building if there's no fire. Private companies like Twitter and Facebook appear to try to hold themselves to a public standard but private companies are allow any standard they please. If you're in a movie theater and start yelling throughout the movie, the theater isn't restricting your free speech by kicking you out.