Your argument is reasonable, until a better way to market to individuals comes along. It's not about the size of Facebook's user base or their reach on the web,

Your argument is reasonable, until a better way to market to individuals comes along. It's not about the size of Facebook's user base or their reach on the web, it's how cheaply and effectively brands can sell their product by paying Facebook to help them do that. Once someone else can do it better, that's when it's game over for Facebook.