geekesse
I think the responses to this thread explain quite clearly why it is ‘brave’ for a person who has hitherto been identified as he/him to ask to be called she/her. It’s really none of my business what a person has between their legs, or what they do with it, provided they do not break the law. If someone wants to be addressed in a particular way, how does it harm me or society to respect their wishes? There was a whole thread recently on Mrs/Miss/Ms titles, and as I recall, most posters were happy to address people with whatever title they prefer. This isn’t so very different.
Which responses do you mean, geekesse? I have seen neutral comments, such as people saying it wasn't 'brave', but nobody saying that it was anything negative.
A number of people, myself included, have said that they aren't bothered either way, which, as you say, is exactly how most people feel about those who have not changed pronoun.