I've answered this many times. 1) I'm not so experienced with Yahoo's ID system; 2) I like to protect my privacy; 3) hm I had a third reason but I forgot what it was. It's posted--I think on this board--somewhere.
I will say I'm an attorney admitted in NY and I've never had any sort of ethical complaint made against me. Also, that this is the only ID I use, and I honestly don't try to mislead anyone.
If that's not enough for you or anyone else, feel free to put me on ignore.