Many developers build gated communities specifically for those folks who either are afraid of crime or don't want just anyone being able to drive in front of their home. Many or most gated communities also come with an Association Dues which helps maintain those gates or security or pools and Clubhouses. Gated communities give some a sense of security or others just like the fact that fewer Jehovah's witnesses or sales people come to their doors. Some look at it as snobbish. Some look at it as added protection for their children to play outside without the concerns of an open community and others still just like controlled communities where they limit access to a "select" few. Whatever the reasons most emergency people (Police/fire/emergency) have key cards that allow access and others, that are really exclusive, provide for 24 hour security employees that are at the gate and can allow entry to emergency vehicles.
Personally I don't see a need in this area. Cities like Atlanta, Birmingham, Nashville and even Madison or Huntsville you'll see more of a need or desire for it but still there are people that just like feeling exclusive and will pay the money for the ability to live in one of those communities. I hope I never feel I want to or have to live in a gated community.