I have to say that they have good and bad points.
Pro - Keeps kids off the street......
Con - Th3Y ar3 All pLaYed by 14 YeAr OldS wHo TyPe L1k3 Di5
Pro - Provides social interaction. In this day and age where every parent is too scared to let their kids go to the park because the TV says they will be raped and murdered and become addicted meth, it is important kids learn the fundamentals of conversation and develop people skills somewhere and these games provide such a forum.
Con - People spend all day playing them instead of developing social skills (Counterpoint to above)
Pro - Brings people of all nationalities and cultures together
Con - They have trashed my credit card
Pro - Keeps all the geeks off the street, who wants packs of RPGers terrorising the neighbourhood.
Con - Keeps all the cute geek chicks inside so I never meet them
Pro - Allows people of all ages to interact. Seriously you have most age groups represented (I have never me anyone in them in the over 60 bracket but I'm sure they are out there somewhere).
All in all, its mostly about moderation. Parents should be keeping track of just how long their kids are spending on certain things, just as adults should have the ability to regulate the amount they spend doing it........