If I ever deleted mines, could be due to:
Fear that some enemy will find them and use them against me somehow.
Fear that other people I know will read and judge me.
Fear that people will misunderstand my words and get mad at me.
Fear that my post was stupid, makes no sense and people will laugh.
Myself hating my own post because I think it's foolish and idiotic. It happens with the old posts, usually. After some time, i look back at them and said "I can't believe I said that =/". I know there's probably nothing wrong with them, but I can't help but thinking I've screwed something up.
At the moment I haven't deleted any post... I'm trying not to worry too much.