I see a lot of people still only want to be known on a first name basis. I'm not sure what the fear is. Amazon encouraged real user names awhile ago and now Google is implementing real names into YouTube (which in theory should cut down on all the stupid comments (racism, etc.) especially when maybe potential employers will start scanning YouTube comments). Problem is it's entirely optional right now and I see very few people on YouTube using their name.
For me it's not a fear of letting my name be known, for me I just don't like my name much. I guess being around it for 19 years, being surrounded by similarily named people, it seems boring and bland.