He's entitled. He earned an honors degree in economics and he has a Pulitzer Prize.
But what qualifies him to speak on this subject is his medical degree from Harvard and his board certification in psychiatry by the American Board of Psychiatry and Neurology, plus his tenure as Chief Resident in Psychiatry at the Massachusetts General Hospital. During that time, he and a colleague identified a syndrome associated with manic-depressives which is now part of the standard works on bipolar disorders. His seminal paper, "The Epidemiology of Mania," has much to say about BDS, even though it was written thirty years ago.
He served in the Carter administration and was a speech-writer for Walter Mondale.
Unfortunately, there is no cure for BDS - it can only be controlled. And if BDS did not exist, supporters of the current administration would have invented it. As Eric Hoffer said: "A mass movement can exist without a god, but it will always fail without a devil. Every mass movement must have something to hate."