This is at its root a question of the morality of democracy, and the answer isn’t as simple as pro-democracy Western liberals would think. The issue is if it is fair for a rural majority north to essentially rule the tax policy of a minority urban south? If you were from the south, would you be fine with supporting a massive redistribution of wealth from a centralized and disconnected government? Just because it is democratic does not make it fair.
I am a supporter of democracy, but it must vary from region to region. One region’s answer is not another’s. Thailand needs a more federalized system with a weaker central government. Let the different regions have more self-autonomy.