demons are necessary

Had a simple insight today.. Often I have wondered why asuras (ungodly) species or beings are said to live in some of the supra-earthly or heavenly planets mentioned in the Vedas.. Why don't ungodly humans all simply just descend down the ladder of consciousness and enter into sub-human bodies, societies, lokas, etc? Why are some said to be higher than humans, in the cosmological sense?

Because, I figured, they are necessary to maintain balance in the universe. With the cycling of the yugas, naturally agents of decomposition must take up the occupational duties which issue forth from Lord Visnu or, Lord Ananta. In other words, humanity's demonic overlords wax and wane in their power and population in accordance with the amount of godlessness in human society. It is not unlike the waxing and waning of organisms in the compost pile in your backyard.