Voldemort And The Death Eaters

I think Voldemort should be thrown into Azkaban for ten years, and the be be-headed when he gets captured. And also, people need to start using He WHo Must Not Be Named's name! I think the Death Eaters should befall the same punishment. They are just as horrible. I wonder what made them and Voldemort turn to the Dark Side?

Absolute power corrupts. When Valdemort realized he was stronger than most wizards, it didn't take much to convince himself that he could make his own rules. Those who want the ability to make others suffer were drawn to him like a magnet. The Death Eaters were born. They were greedy opportunists who believed that others were too stupid or too weak to follow Voldemort.

What I don't understand is the Dementors. What is the point of them in any world? And why would "good" witches and wizards tolerate them, no matter how useful they are?