Outrage supposedly felt on behalf of others is extremely gratifying for more than one reason. It has the appearance of selflessness, and everyone likes to feel that he is selfless. It confers moral respectability on the desire to hate or despise something or somebody, a desire never far from the human heart. It provides him who feels it the possibility of transcendent purpose, if he decides to work toward the elimination of the supposed cause of his outrage. And it may even give him a reasonably lucrative career, if he becomes a professional campaigner or politician: For there is nothing like stirring up resentment for the creation of a political clientele.
Antiracism is a perfect cause for those with free-floating outrage because it puts them automatically on the side of the angels without any need personally to sacrifice anything. You have only to accuse others of it to feel virtuous yourself. There is no defense against the accusation: The very attempt at a defense demonstrates the truth of it. As a consequence of this, it is a rhetorical weapon of enormous power that can be wielded against anybody who opposes your views. It reduces them to silence.