No one really knows the depths of what it takes to become addicted, so it's basically guesswork. My own personal opinion is that it's less about genes, and more about social patterns and the early years of development. Even so, I've witnessed socially amiable and very active people become addicted, in the most subtle and surprising ways. It's never really a clear cut thing, trying to define what makes people self-destruct.
About people who don't do anything for themselves, you'd have to be ignorant to truly believe people WANT to ruin their lives. It takes effort to break a strong addiction, and for that you need surplus resources and motivation. Not everyone has those things, and I'd rather try and help them than just ignore it.
It's not my responsibility to help, nor do I feel "good" when I try to counsel against MMOs. I simply believe it's for the best - and as such I will always advocate helping others, whether they "deserve" that help or not. If I can help a single individual against addiction, I will consider it worth it. Fuck guilt, blame, taking credit for helping, and all of those irrelevant things. Focus on what helps.
That's my opinion, anyway