IMHO I'd go to talk to them about it, but if you are maintaining friends, keeping your grades up, and want to play in your free time then I can't imagine what problem they would have other then a general dislike of video gaming. To me this is a hobby just like I enjoy painting and other activities that have no "real" goal or purpose other than I have fun doing them.
There is a great web site that explores the psychology of MMORPGs - both the good and the bad. It examines the very real social worlds of the games (such as how it could help or hurt your relationships) as well as gaming addiction. A good listing of articles by topic can be found
here.
This is a great article on the very social nature of MMORPGs and how they are much more like hobbies than more passive forms of entertainment.
Here's an intersting site on gaming addiction and its effects.
Hope these are helpful. Maybe you could print out some of these to show your family and friends to help them understand your hobby. If you can show professional psychologists talking about these games in a positive way, maybe they will be more supportive or at least more tolerant.
Good luck!
