I may want to erase some posts that I felt safe having up there. I no longer do if you're opening it up to just anyone.
This is why opening up secret boards may not be the best idea. I once was invited to join a secret board on a forum once (which I did) but soon discovered that, because of a lingering animosity toward me on the part of some members there, the decision had not been unanimous. This changed the tone and the dynamic of the secret board to some extent and the posters in question started limiting their input there. I didn't take this personally but, after my initial few contributions there, I chose to respect the fact that these members were there before me and considered this their safe haven and I therefore stopped visiting that particular room.
Admitting folks that you're reasonably sure will respect the P in PI isn't enough, I think. If natural antagonisms hold true on the public boards, there's a likelihood they'll hold true on the secret ones, as well. This defeats one of the main purposes of a secret board. People wouldn't be able to feel they can let their hair down (if they have any).
You want to get closer to a poster? Then engage in a private conversation with them.