We should have the ability to delete our own Pms. I cant see why we would have to even ask for it.
We should also be able to edit our own posts at any time, the post should show when it was edited and who by and also a drop down box when doing the edit to select the reason for the edit including "removal of personal information". Most other forums i use allow all this.
Sure some would abuse that to alter their poor forum behaviours, but they would be in the minority.
reddit doesnt let you delete stuff inc PMs and is a huge turn off for me in using it.