I made this change a little bit ago. There were a few active threads on this site that I would have preferred to have remained, but with the way it was previously set up, whomever started the thread had the power to delete the entire thread, including ALL of the messages anyone else posted within it.
Not sure this is the best way to prevent that from happening, but it put the brakes on it until I have time to think of a better way to handle it.