Categorism As a Dirty Weapon
Categorization can be used as a weapon. A way of establishing social norms and hierarchies. Distinguishing what and who is acceptable from what and who is not. When a human being kill another human being, we usually call this a murder, and condemn the killer by categorization them into the category of "murderer". In many cases, this is fair and reasonable: To kill other people is to deny them their right to life, which we have every reason to condemn as a very bad thing to do.
However, lets say that we suddenly expand the category of "murderer" to include people who actually haven't killed anyone. For example, lets say that a group of activists really hate computer games and the people who play them. Lets say that this group starts using the term and category of "murderer" about anyone who has ever "killed" a fictional person in a game. They establish the idea that if two persons play a game where they kill each other in the game, this makes them both murderers - never mind that both "victims" are very much alive and that they by the way consented to participate in the game and did enjoy the game. In a case such as this, the categorization has become categorism. The weapon has thus become a dirty weapon, unfairly stigmatizing innocent people.
Categorism is not always used as a weapon. But when it is, it should be considered a dirty one.