The ruling class does not want people to talk about certain issues that would bring them to understand how they are controlled, abused and deceived. The discussion about differences is a sensible way to avoid serious conflicts and physical confrontations but the rulers want the people divided into quarreling groups that fight each others and cannot rise against their oppressors.
First, people are divided into groups set up to be hostile to each other by favoring some minority group and giving them disproportionate positive publicity. Then discussion and especially critique about issues related to the group is prohibited. Examples of barrier concepts when related to different kinds of people, their ideology or bad behavior; antisemite, antivaxxer, islamophobia, homophobia, political incorrectness, denier of the official propaganda, hate speech etc.
The rulers want all conversation to avoid their crimes and nobody bringing up any real problems in the society; 911, money as debt, usury, war, drugs, government complicity etc. In the end we are supposed to discuss about something "safe" like subnavel activities, organs, body cavities and their products, decadent behavior and how proud we are about it, how triggered we are and so on.