We’d like to think we do our best to help out the less fortunate among us. At what point, though, do we harm ourselves in the process? This hour, we’ll talk about extreme cases of philanthropy with New Yorker staff writer Larissa MacFarquhar, author of “Strangers Drowning: Grappling with Impossible Idealism, Drastic Choices, and the Overpowering Urge to Help.”