Actually, I don't keep a lot of my life anonymous and secret and the bits that I do, I do out of fear and shame.
I don't think that is strictly true.
I think you keep a LOT of your life hidden our of practicality, caution and simply because some things are irrelevant to certain people. You were the first person I heard use the term "inappropriate self-disclosure".
To me, privacy is important. You can't disclose things about yourself with all the relevant background very easily. If for example I was to disclose that in the past month I have built up a huge collection of pictures of legs on my PC, to post into a forum discussing themes surrounding a movie about gay cowboys, I don't most people would understand what that was about. I'd have to explain first of all the BBM phenomenon, Penny's interest in the forum and community, my own foray into writing and getting to know a few people, the Bar, the Lex hour, the Legs Hour... and even after all that they might still remain a bit dubious.
Things only make sense in context, and it can be more effort trying to explain the whole context to people, than simply enjoying the freedom to have private things. People can only form a relatively simple picture of "who you are" and privacy is a way of filtering out the things you don't want to have to explain to paint a working picture of what sort of person you are.
In yet another way, secrecy is important to keep yourself from harm. There's a certain owner of winged monkeys who did her damndest to get our physical address: information I am not comfortable with sharing. I guess that might be classed as "Fear" that some crazy person is going to cause us trouble, but I think merely that it is caution that stops people shring all the details of our private lives.
Finally some secrets are
fun to keep. Example:
Secret text:
My secret is 'what I am going to be wearing when you stop refreshing this page and come to bed, sweetheart' 
Night night folks!
