I am in a similar situation, although much less extreme.
I've had some issues with game compulsion (thankfully they haven't harmed me as much) and I've also faced that ethical dilemma when I decided to get into indie development (as a hobby).
If you're willing to enter the industry of MMO development, I think you should forget about those "ethical" design principles right away. Most MMO are designed with operant conditioning in mind; they're glorified Skinner's boxes. Even when a feature appears designed to enforce casual play (think WoW's "rested" system) it is often implemented with the idea of giving hesitant players an incentive to log in. "I don't really feel like playing, but I should have a full rested bar by now so hey".
Not even EvE online, which has been jokingly referred to as a game that doesn't want you to play it, is free from this sort of stuff. Okay, mechanically it may not necessarily reward obsessive players, but it is built with social interaction in mind, and you will eventually get to a point in which your corporation requires your presence.
If you want to develop in an ethical way, I think MMOs are a complex issue. It is unlikely you'll get to lead the design of a MMO without doing a lot of grunt work first, and even if you do, it's doubly unlikely any publisher or investor will back a risky enjoy-but-don't-get-addicted scheme. However, there are many other genres that are focused on giving the player a great experience, without attempting to condition him or her to become a slave.
That said, some people will become addicted to anything, and you shouldn't let that reality haunt you. Just think of the quality of the experience. What makes it compelling? If it is addictive because it is a blast to play, rejoice. If it is addictive because it deliberately exploits the way your brain reacts to short term rewards, social pressure... Then you have a problem.