Anything you write here, whether in public or private, can be seen by the people who run the place.
Your identity can not be known unless you tell someone, although the people who run the place can look up what your IP address is. Once you set up an account, there’s nothing you can do about that.
If you want to keep something truly private, do not put it anywhere on fluther. Or any other website for that matter. The feds can make the web sites cough up anything you write if they want to.
The moderators here are allowed to investigate issues that take place in private messages. They can not read the pms, but Augustlan can. So treat people nicely in private just as you do in public. There won’t be any trouble.