Why aren't voluntary response samples usually representative of the population?

Which is the best rebuttal to the following counter-argument? playing video games can be beneficial to youth because it enhances their hand and eye coordination, sharpens their reflexes, and keeps them out of trouble if they were playing outdoors. a. playing video games can be harmful because it is often done in isolation, which hinders the development of social skills b. playing video games can be harmful because excessive playing can lead to obsessive dependence, which can be dangerous. c. playing video games can be armful because it deprives kids of healthful exercise they would normally get by playing outdoors. d. playing video games can be harmful because the more attached youth are to the games, the more detached they become from reality.