Provoked by a post by my friend Roger Calver over on the RPGSite.
What is a roleplaying game? This depends greatly on who you are asking. Some people want to limit the definition to only include games which include certain characteristics. This is a litmus test definition, or definition by edges. The problem with definition by edges is no matter where you put the fence, there will be something that ends up straddling it.
I prefer to define by center - i.e. X is a thing like this. Thus, the definition from center for an RPG would be something like "An RPG is a game where you play a role". I think the problem with this for some people is that it lets in a lot of things they'd prefer to keep out. Fences are for keeping what is inside in and what is outside out. Borders need policing. After all, something may be slipping inside that fence!
Humans are very territorial, or at least the cultures I am familiar with are. Sometimes this idea of territoriality gets sublimated into other things not associated with real estate, like intellectual and social turf. It always comes down in the end to fear. Fear that the Other will get inside that fence and destroy what is safe and ours, like a weasel in a henhouse.
So what's to prevent that weasel getting in without the fence? Nothing. Nothing at all. Weasels can come and go as they choose. I think there is more harm in marking and patrolling that ideological fence then there is of weasels raiding the henhouse. This harm comes from bitterness, anger, and divisiveness. Each time we make a fence, we subdivide our mental landscape until we are all kings of a quarter acre. We get niggly and mean-spirited, suspicious and paranoid. I tend not to like hanging out with folks like that, personally.
You would think that we tabletop RPGers would remember how we cut off those horrble computer RPGs from our communion - after all they were different! We showed them! It was like sawing a limb off a tree - but from the wrong side.