Personally, I just can't buy the dementors. They're overpowered, over the top, they don't work.
First, they feed by taking people's souls out, and making their empty bodies into dementors themselves, right? Muggles can't even see them. The only way to fight a dementor is the Patronus spell, a very advanced magic few wizards can master, and even then it just repels and subdues. Nothing apparently can destroy a dementor.
So, why aren't they ruling? Logic says that anytime there's the slightest faltering in the wizard community, the dementors would swamp the world and create a supernaturally charged omega-man type situation.