First, it's offensive because I am not a man.  I have enough trouble with the world accepting me as a woman to have the medical community continue to label me as a "man".  If they want to track the HIV and AIDS risks for IS/TG/TS people I'm all for that... but don't dump us all in the category "male".  You talk about HIV risk factors being more important than "identity", well, then why don't we just lump all heterosexual women in the group of MSM because the number of people infected every year is identical between MSM and women.