Why the anonymity?
There's a few simple reasons, really.
First off, in my real life, I live stealth. My goal with transition was to just live my life as the woman I am, and that's what I do. I really don't tell anyone I am trans, as the vast majority of people have no reason to know.
Second -I've seen what can happen when you disagree with someone who's thrown ethics in the bin. Long gone are the days when insulting your opponent is satisfactory. Now, some will locate a person and falsely send SWAT, or go harm them in person, or send everything to friends, family, one's employer - literally out to ruin one's life. That's just the world we live in now.
Third - The things I talk about under the Tranime persona just aren't the focal points in my day to day life. Sometimes, I wan't to just mute Twitter and go play on my NES for a while. Keeping the debates under a persona I can just log out of allows me to balance it against the rest of my life, and prevent it from being a distraction when something else calls for my attention.