We do not think any topics should be "off limits" except those that deal with illegal activities as stated in the current rules. Having said that, the moderation staff in OT have wide latitude to end a discussion if it becomes toxic or descends into name calling, flaming and/or trolling. From what I have seen, thread starters need to be very careful what they say when starting a thread on a controversial subject because how they begin the thread has a great deal of impact on how it will progress.
These are discussion forums, not argument forums. In reading reports and checking on some threads, in general, they often start fairly well and then two people get into an argument and the thread degrades because instead of listening and discussing concepts with civility they begin trashing each other. Once the personal digs start, it rarely ends well. Our Moderator's primary responsibility is to see that civil discussion is maintained. Once the thread becomes uncivil, they are called to act and often closing the thread is easier than trying to infract everyone and then put up with all the whining that follows in PM's, each side seeking its concept of justice against their opponent in the thread.