"Nobody"? It has been directly implied a couple of times in the thread...
Since I was the person who made the first post, let me clarify what I meant:
Depicting the Prophet Muhammad's face is simply
Not Done. Steps have been taken to avoid doing it (it is the only portrait in the game that is not shown for this reason), and people would be rather upset if that had not been the case.
I suppose you could keep that property in place while having him alive, but that leaves the rather obvious issue that something bad (torture, mutilation, etc.) could be done to him while he was alive (which wouldn't be easy to block completely), that something bad could be done
as him (e.g. joining the Devil Worshippers or converting to another religion) by the player or AI (which would be hard to
completely block), that he could pick up (objectively or subjectively) bad traits/modifiers, and things like that. Those things would
rather understandably be something that
easily would upset people and could have negative consequences (to one extent or another; someone posting a negative review on Steam is
a negative consequence that could arise), particularly when taken out of context or blown out of proportion (e.g. a random player deliberately sets out to do something bad to the Prophet Muhammad, posts the results on Reddit (where the CK2 subreddit isn't moderated by Paradox and they thus aren't guaranteed to be able to get it removed (like they could do with something bad posted on the PDS forums)), and some newspaper picks it up and writes an article with the headline "CK2's latest expansion lets you do [bad thing] to the Prophet Muhammad!"), so the
prudent course of action would be to avoid those issues by simply not having him alive during the game.
As for the examples you listed of other bad things already in the game, they're rather different:
- The "Mad Arab" example is something I've not seen before (or at least not something I've noticed; I don't believe I've ever had a GHW against Muslims in my games, since most of my pagan reformations have been Norse ones I carried out myself and I didn't have any interest in attacking Muslim areas of the map with GHWs in those games) and also seems like something that's being said in-character by the attacker. Maybe it could be reworded a bit, though, to make it clear(er) that it is the Fylkir/whatever that's using that wording (or reworded to not include that line at all), in case someone doesn't like it.
- You can convert
any county away from/to any religion/culture in the game (and might not be 100 % successful, considering minorities aren't really portrayed), and with the exception of the holders of a few titles that always exist (e.g. the Papacy (which is used for maintenance stuff) and various mercs (some of which I believe are Muslim, by the way))
all faiths can be eradicated, so it isn't something that's directly targeting the Muslim religions. Sure, someone
could be upset by the specific scenario you mentioned, but I'd argue that it is less likely to upset people than anything directly involving the Prophet Muhammad.
- Having a distant descendant of the Prophet Muhammad (that, aside from the characters that are alive at any given start, will be completely fictional characters to begin with) do something bad (or have something bad happen to them, or have/get bad traits, or whatever) is a
bit different from having him do something bad (or be the victim of something bad), considering that they're not regarded in the same way. Again, someone
could be upset by it, but as with the above example I'd say it is less likely to upset people than something than could happen in the Prophet Muhammad was in the game and something bad happened to him/he did something bad/etc.