Dungeons & Dragons makes no attempt to present itself as factual. It is fantasy, although some lunatics might believe otherwise.
This stuff talked about here... 9/11 inside jobs, aliens doing horrible experiments and whatnot, secret governments murdering and mind-controlling... I don't see conspiracy theorists clearly stating, "Hey, this is all just fantasy to entertain people."
So your comparison doesn't fly, regardless of whether some nerd goes nuts and stabs other players with his magic dagger. It simply doesn't compare because TSR/Wizards of the Coast are a game company clearly making games.
I don't see these conspiracy theorists saying anything like that. Everything they do is geared toward exposing supposed hidden truths, not to entertain with magical fantasy stories and settings.
"I can conceive of nothing in religion, science, or philosophy, that is anything more than the proper thing to wear, for a while." ~ Charles Fort