The arguments the gang "expert" made about similarities between D&D player organization and gang organization would apply equally well to many organized religions, such as Catholicism. I wonder if a prison could get away with banning that?
The only part of the argument which got quoted in the article is that in D&D, some people give orders to other people, and in that way, it "mirrors the structure of a gang". Which is an argument that would encompass not just religion, but all sorts of other things. In a poetry group, one prisoner tells the others that today they'll be writing sonnets. A sure sign of gang activity! In fairness, there may be more to th…
On the other hand, the NPCs would probably agree that the PCs rampaging through their world are pretty ganglike.