[AndyKelley]

The only point I can think of, and which I tend to agree with, is that when you do it you make a big fuss about the gender of the person and that distracts from the actual content that you are writing about. So opponents of using "she" as the default sometimes may be simply annoyed that the author is, instead of just using the already established convention, breaking convention in a noticeable way that might distract from the real content of the document.