Each main Legend of Korra villain represents a different political ideology.
Even the more minor villains like Varrick (who is not always necessarily a villain) and the Earth Queen represent ideologies as well: Capitalism and Monarchy, respectively.
"Only the Avatar can master all four elements and bring balance to the world."
Toph: Alright, what you need is a good old fashioned back pounding to relieve your stress.
Aang: Pound away.
Toph: Okay, if you want me to bend out this metal, you need to relax.
Korra: I am relaxed.