I wrote a paper on the repugnant conclusion as a graduate student and Derek Parfit reviewed the paper and recommended rejection. Parfit had no trouble being respectful and constructive. And I was honored and greatly helped by his three pages of single-spaced comments. Also, I don't see any problem arising from the disparity of power between us. Given it was a rejection, there was no pressure to be deferential. The only other time that I remember a journal reviewer identifying his or herself was another very famous philosopher (still alive - so I won't use his or her name) who recommended revise and resubmit but who wasn't at all heavy-handed in his or her comments. The reviewer made clear that he or she could be wrong on various points and was open to being convinced otherwise. In any case, I don't really see the discrepancy in power to be a major concern. After all, at conferences and workshops, there is often a huge discrepancy of power between the audience member voicing some criticism and the author/presenter. And I don't think that it would be better if audience questions/criticisms were presented anonymously. And I know a lot of people who have no problem being quite up front and honest in their criticisms even when their identity is known. So I think that it's often okay to reveal your identity, but that you certainly mention things that one should consider before they do.