Now, should it be secret? That all depends on you, but be aware that it's not likely to be a secret or anonymous forever. I know that I'm pretty proud of my writing skills, so I am anxious to show my blog to people. At some point you lose track of who all you've shown it to too, and who they might have shown it to as well. I guess I figure why write it if you're not going to share it? Sure, random people may come along, read it and proclaim it to be the best thing they've ever read, but frankly that doesn't happen often. It's like buying the perfect outfit and never going out anywhere in it. Scan through my posts, I've written some fantastic stuff (or so I think) and very few comments. Only a few from anonymous posters that we'll assume tripped over me. You're likely not to be discovered as the next pop sensation while singing in your shower, and you're not likely to be revered for your prose hiding it somewhere on the Internet either.
Ok, so say you make a blog and you post links to it on your Facebook page. What if you want to write a rant? Happens to me all the time. All I can say is that just as some things are better left unsaid, some things are better left unwritten as well. Here's also a place to work on your writing and your communication skills. Explore why you're angry or upset. Blog about that. Maybe it'll open up passages to conversations you've been putting off. Maybe it'll help you realize what's really troubling you. I don't mean to sound sanctimonious, but writing (and blogging) does these things for me. I should do it more actually, it might help.
Don't be afraid of who you are, or of sharing that with people. We're all a work in progress. :)