Morality of Using NX

...seriously? You play the game. You haven't quit because "they rarely listen to their customers." They are providing a service for you. There is nothing immoral about paying for the game. If you don't want to pay for NX, that's fine, but it's kind of stupid that you're trying to play the game and protest the spending of money on it at the same time.

Side note:

The second the cards are activated Nexon has already made the money. Shuffling it around a little isn't giving them money, as they already have it.

True, but using MTS creates more demand and gives the people that buy your items with NX more incentive to buy NX, and thus they will buy larger amounts of NX. At the same time, it takes a small amount of NX out of circulation for good, which adds up to a lot of NX spent on tax alone.