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

In the real world, anyone who wants to redistribute/re-sell a company's products for commercial gain is legally obliged to pay distribution rights/royalties/whatever, if not, at least sign a contract of sorts to gain the privilege to do so. Of course, people get away with not doing it 99% of the time (especially if you're a small business) but that doesn't mean it's okay.