Brought to you by Penguin. The origins, consequences and limitations of an ideology that has quickly become highly influential around the world. For much of their history, societies have violently oppressed ethnic, religious and sexual minorities.

It is no surprise then that many who passionately believe in social justice have come to believe that members of marginalized groups need to take pride in their identity if they are to resist injustice. But over the past decades, a healthy appreciat...