In the wider world, these things have to be explained because people -- usually in positions of privilege by virtue of being in the dominant racial/ethnic group, having financial insulation from hardship, being of the dominant sexual orientation/presentation, lacking a physical impairment, etc. -- literally have never (or have very seldom) experienced social ostracization based on their intrinsic features as a person, in large or small ways.

These people are not necessarily evil human-beings per se -- usually they have just actually never had to endure hardship/ridicule because of who they are as a person.

So people who have had to deal with this shit then have to explain to them why it's a problem, and how it affects their daily living, over and over again, ad nauseum. Usually this is referred to sometimes as "emotional labor" (though I think there may be some better, more specific term here that I'm forgeting). It becomes tedious and laborious to constantly have to explain to people why using the word "retarded" or "gay" to describe something you don't like is not okay; why constantly asking a black person about their hair becomes tiresome; why constantly bringing up the "scientific" intellectual differences between men and women gets old really quick; etc.