Atlanta has the 3rd largest LGBT population behind SF/Seattle and is pretty diverse in general. It's the other parts of Georgia that can seem backwards. Same goes for North Carolina. A person from SF would feel at home in Asheville or Raleigh despite everything going on in the news.
Cobb County (immediately west of the city) also (a) is unwilling to contribute to MARTA, (b) has a terrible traffic problem, (c) is currently burning money to build an overpass over 30 miles of existing interstate to solve the problem forever (see: http://www.ajc.com/news/local/mile-reversible-toll-lane-what... ), & (d) refuses to even consider rail.
From wikipedia [1] Atlanta has the 3rd largest percentage, but it's 11th for total population. Admittedly those figures are for 2005, but I wouldn't expect Atlanta to make up that much on the top 3 in the last 10 years?