So come and create your very own LiveJournal. Let the world know the story of your life, as it happens! (Whether they want to or not!)"
~from the LJ homepage
Now, I don't want to get off on a rant here, but...I think an online journal is kept public and online for one main reason--to tell other people what is going on in your life, how you feel about stuff, whatever you choose for them to read. If you have something you don't want everyone to read, then you make it private. Private journals are kept for the writer; online ones are kept for the reader.
But that's just my opinion. I could be wrong.