Tough question.
Not sure that censorship vs free expression is entirely the issue, though. Since this is a privately owned and operated site, the owner pretty much has final say on the content.
Thing is, the line can be pretty blurry. After all, it's possible to have a discussion with a fairly mature subject and dialogue, yet that does not have any actual profanity or other overt references. In the eyes of some, such a discussion is not suitable for younger folks (I know of some to whom teenagers aren't allowed to engage in such discussion).
Additionally, I know of some teenagers (for example) who are more mature, and better able to cope with such dialogue than are some 'adults'.
Profanity isn't such a clear cut subject, either. With some exceptions, some of what is termed profanity can be, in another context, merely descriptive, or even harmless. On the other hand, it's perfectly possible to completely insult and denigrate someone without a single word of profanity.
I think the best method is to have some basic ground rules where certain behaviour is not tolerated (and that may include specifying certain words or phrases as off limits, which, while not necessarily always bad, rarely lend themselves to mature conversation), and enforcing that evenly across the board.
One of the earlier polls done here determined the average age of the participants here, and we're generally a bit older than those among other fora of this type. Hopefully, that also translates to a bit more overall maturity as well (and by and large, that's what I see here, and what I like about it).
Certainly, there's no pleasing everyone. No matter how strict (or not) the moderators here try to be, there will be someone who is displeased, in one direction or the other, about the content on this board. I personally know adults who would blow a fuse at the earlier creation vs evolution thread we had here a while back (not the thread per se, but the mere thought of discussing the idea), let alone think it was appropriate for children. And it was much more mild than similar discussions I've had on other boards.
Personally, I've had no reason to think that the administrators here have done anything but the best that they can, nor that they've been anything but evenhanded.
I don't think that there's any hard and fast line to be drawn, apart from a few good rules. Mostly, it's going to have to be judged on a case by case basis. There will be some obvious offenders, and there may be some dialogue that should stay, even if it isn't entirely unoffensive. I think the context of the discussion should influence the decision.
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