The reason why it's so famous though (and why some people tend to use it in a tongue in cheek manner) is because "you know it when you see it" is a hilariously unhelpful and capricious threshold, especially when coming from the Supreme Court. For rights which are so vital to the fabric of the country, the Supreme Court recommending we hinge free speech on—essentially—unquantifiable vibes is equal parts bizarre and out of character.