Trying to put my finger on why I was intrigued by this letter and response, since the answer is so straightforward, and I think it has more to do with what isn't in the response than what is. (Sorry if this isn't completely coherent – it's very late here and I'm tired.)
As I read it – and this is reading a good deal into LW's words, so I could be wrong – the question boils down to: "At what point are the negative consequences to my personal life of fulfilling a particular ethical obligation in my professional life severe enough that I would be justified in not fulfilling that ethical obligation?" And it's fascinating to me that Appiah doesn't actually explicitly acknowledge the personal cost to the LW. There's a brief consideration of the appropriateness of giving the friend notice before reporting, out of special obligations to a friend, but nothing about the loss of the friendship.
Obviously, there are points at which personal cost does actually outweigh professional ethics. (As an extreme example, suppose it's a choice between refraining from reporting the friend to the board of medicine and literally dying; I doubt most people would blame LW for not reporting in that scenario.) But by not explicitly acknowledging that the loss of the friendship could even be a factor in that sort of balancing of interests and obligations, Appiah seems (to me) to imply that wherever the line is beyond which personal cost can outweigh professional ethics, LW's situation doesn't come remotely close.
no subject
As I read it – and this is reading a good deal into LW's words, so I could be wrong – the question boils down to: "At what point are the negative consequences to my personal life of fulfilling a particular ethical obligation in my professional life severe enough that I would be justified in not fulfilling that ethical obligation?" And it's fascinating to me that Appiah doesn't actually explicitly acknowledge the personal cost to the LW. There's a brief consideration of the appropriateness of giving the friend notice before reporting, out of special obligations to a friend, but nothing about the loss of the friendship.
Obviously, there are points at which personal cost does actually outweigh professional ethics. (As an extreme example, suppose it's a choice between refraining from reporting the friend to the board of medicine and literally dying; I doubt most people would blame LW for not reporting in that scenario.) But by not explicitly acknowledging that the loss of the friendship could even be a factor in that sort of balancing of interests and obligations, Appiah seems (to me) to imply that wherever the line is beyond which personal cost can outweigh professional ethics, LW's situation doesn't come remotely close.