As others touched on, if somebody has an addictive personality then of course MMORPGs will cause issues. However, if it is no EQ, for example, then it will just be something else. One can be responsible and still play those games.
I have played EQ since 1999, not too far after release, and I still play it. In fact I am in an end-game guild (uber guild if you want to use loser l33t speak), my druid has more hitpoints than the typical warrior on our server, but I have managed to have a 'real life' outside of EQ. I managed to get through college, go to martial arts twice a week, go to the gym (okay have slacked off on that) and worked ~45 hours a week.
People can play those games reasonably well, but those clowns that quit school/work/social life are just losers to begin with and it has nothing to do with the game. They have other issues and EQ/DAoC/AC/UO is not the issue.