PS- Don't tell people why they should play games. There are many different groups and reasons why someone plays a game. If I couldn't make money here I wouldn't be here and I would be off fighting The Good Fight in one of the other games that I also love. For me though my carrot is being Uber one day and Money. Don't try to take away any of my carrots because they are delicious.
And about that...
10+ M people still play Blizzard's MMO. The shiniest items are bound and not even tradeable. Gold selling is clearly disallowed and gold seller (and buyers) are constantly banned. So no, not all players or even most players, play for money; sure, maybe the hardcore players do, but definitely not the majority of average, casual players that make the backbone of any MMO.
Also, not that I want to be rude or anything, but if you say that you are here to specifically make a profit (to not say a job, as other people said) out of the game and instead of bringing money into the economy and contributing to server costs and company profits, you want to take money out of said economy (money that have to be paid by other players) in what way you leaving would make the game world/economy worse? All I can see is that the remaining players would lose less because they wouldn't have to subsidiaries you're winning anymore (on top of paying for game expenses and MA profits).
Sure, more players are good for the game, but only as long as each of those players brings its contribution towards covering the server mainenance, development costs and company profits. When someone instead of contributing is taking out money, how they are helping the economy, the game, the company?
Let's say (random number) that the maintenance, development and MA profit sums up to $100,000 per month (again, random number). Now every player that is a net depositor, contributes to this, in a larger or smaller percent (some may contribute with thousands, while others may contribute with only a few bucks). When you neither deposit or withdraw, you're actually a little burden, since you consume server resources that you're not paying for, but let's say that this is OK, since servers would function anyway (it become a problem only if non-contributing players number would be really high). But when you want to make profit and be a net withdrawer, getting, dunno let's say $100 per month, not only that you're not helping with the cost, but the rest of us have to also pay your $100, on top of MA's $100,000, so our cumulative total cost instead of going down because we have one extra player, goes up to $100,100. How does that help?