Would it be morally fair of Nexon to ban buyers/sellers of NX? I think not.

My point of view is that if its against the rules, dont do it. End of story. So to me, yes, it is "immoral"
However, allow me to ask a (slightly) differant question: "If you had the power to change the rules, would you make it OK to buy/sell NX?"
My answer to that question would be anything that allows the game to continue functioning (ie; the loss of NX buyers does not drive nexon to bankruptcy), and makes the game a more positive experience for the players, should be allowed

Of course, that opens the door to the question of "what if it does not drive them to bankruptcy, but forces them to fire GMs due to budget cuts?" in essence makeing the game overall worsel