They're not legally obligated to censor the fact, but with the way society is structured these days, I think there's an unwritten social obligation to do so, at least in terms of social media.

Business monitor their employees social media accounts, and when you bring negative things to those places, you take a great deal of risk. Its the unfortunate reality of a world where you no longer have a private life, in any place or at any time.

People like to joke, and jokes usually aren't nice: hence why they're kept for close friends. Sometimes people make jokes in public without thinking about the situation, and sometimes other people can hear them. Yes, they can get offended, and yes they can speak their mind, but they shouldn't bring it to a place where the joke becomes inescapable.

I'd rather not live in a world where I have to constantly walk on eggshells or risk losing my job. That breeds an environment which stifles creativity and honesty, because you begin to worry about who you offend and if you should ever speak your mind. Its just not worth having a slightly safer space in public.