Mexico is kind of a unique case. It's a large country with very big upper class and a very much bigger lower class with almost no middle class.
The upper class uses the political machinery to preserve their wealth. While Mexico is a democracy, the corruption has been extended to all levels of law enforcement so any kind of real political reform is problematic.
It isn't a matter of race. We've had decades of true democracy in Central and South America, although there have been the recent setbacks you noted. Hell, we're capable of complete lunacy both in North America and Europe with Caucasians in charge.
Caucasians= Liberals?