I don't think there will be more addiction and abuse as we already have. Look at the addicted people of World of Warcraft, look at the abused people of Scientology...
BTW, to have no social contacts is (almost?) always bad.

You don't have to use only one avatar all the time, and you won't. You probably will have a collection of characters, and you will eventually change them while you change your interests and focus onto other things in life or games.

For a developer its more the other way round, if your game has been successful and you build a follow up, you will use the same character, but you will, instead of asking again for the players preferences, load them from a given database of the former game to welcome the player.