> I get that FB is convenient because most people have an account already, but a FB login button would also do the trick for most communities. More than that c

> I get that FB is convenient because most people have an account already, but a FB login button would also do the trick for most communities. More than that convenience, I think it's the convenience of not having to deal with configuring some forum server software and using it. To many people, FB is the internet. Basing a community elsewhere raises the bar of entry for their target community.