But, adding porn does isolate the audience because now all those who don't like it may not buy the game. Period.
Taking into account your own arguments that would mean that if they did not include it people who want it would be isolated and might not buy the game. It's a loose-loose scenario you painted here.
If people don't buy the game because there is no explicit sex scenes, then the game must suck. A well written, well designed game does not need sex to sell it.
So it is not lose lose unless the game is literally relying on sex to sell, in which case, the game is crap and won't survive. Why? Because people who want porn in a game will still likely buy a good RPG that doesn't have sex, but people who don't like porn and don't want it in their games will struggle internally about buying a game with porn in it even if the game is good.
