In the discussion, Adichie said that she believes the left is now an orthodoxy that you have to follow, "and if you don’t, you become a bad, evil person, and it doesn’t matter what you’ve done in the past or what you stand for. You just become evil and you’re demonized."
She talks about what this means for her in the context of being a writer: "So if you write about a white woman, for many parts of the left it’s valid criticism to say you ignored Mexicans and Bangladeshis. And I’m just thinking, No. People have to be allowed to tell the story. I don’t necessarily want a white woman telling the Nigerian woman story."
She and Coates both talk about the challenges in white writers telling the stories of minorities, though cite examples where it was done sensitively. Still Coates notes that there is a history behind disrespectful representation of African Americans. Adichie points out that also that due to being a minority living in a world "steeped in whiteness" she is acquainted with whiteness in a way that white people are not with other races. She says that often people are afraid to ask her questions and so end up saying things that are incorrect.
Sources: 1, 2