The origin, and fate, of demons

Did the angels and demons of Zoroastrianism, Persian religious magic, become our more modern concepts of such? Why does it seem Zoroastrianism is demonology light, Judeo-Christianity is demonology darker, and Satanism is demonology black? It's like Judeo-Christians worked so hard to personify evil, in its king the devil and in its finites applications through his minions, that old Zoroastrian eschatology became perverted, in effect creating Satanism.
I am also struck with the fact that my worldview is somewhat similar to Zoroastrianism, though I am nominally a Christian. Is it because of my background in comparative religion, and Zoroastrianism is a religion which can encompass all deities? Is it my holistic explanation for things, allowing polytheism (the myriad demons and angels and/or all your pagan gods) and monotheism (the one uncreated Ahura Mazda) at the same time?
Personally, I wish Christianity hadn't invented Satanism, as it often seems it did. Then again, atrocity is nothing new; the Christians did not invent that. Thankfully, most of the evil blood rites of previous religions have faded from memory. There are no Celts burning the bodies of their enemies, and no Mayans sacrificing prisoners to dark gods, I think. Satanists are just the kind of people who want that sort of control, objectifying other human beings. They are not a whole lot different from racial supremacists, slavers, chauvinists, and those who fund prostitution/pornography. These are all people who reduce others' humanity for their own pleasure and/or gain. Yes, these are the vampires who walk among us. They feed on the blood of others, be it physical or spiritual.
And yes Dan, religious zealots are vampires too. They want to consider some other people less than human based upon religion. Yes, they may not be doing so to fulfill their own selfish desires. I do not believe that evil has limits. Lawful evil? Please. Someone who is willing to brand millions of people Muslims, to justify taking their oil, or Jews, to justify taking their wealth, seems to have ulterior motives.
Well, I've come full circle. I used to believe religion was false, and now I'm beginning to again. I still believe that Jesus Christ offers us the best hope for a peaceful future, provided that people quit taking things out of context, stop planning for the Apocalypse, stop religious violence, and start treating each other like their sins are forgiven.
We must all personify God's love and desire to save each one of us. Each human being is valuable to God, and should be to each of us as well.
We're brought once again, through the above musings and through today's news of a woman found guilty of dismembering a lover with a chain saw, to the question: Why is is evil in the world? Who is responsible? If humans can't fix it, stop it, or remedy it, who do we turn to? The religions of the world seem to agree: evil is in the world because a higher power wants it to be here. They also agree that people are responsible, until they repent or are exorcised or perform the appropriate ritual, for the evil they commit. There seems to be agreement that the powers of evil are strong, but man has free will, and the powers of good are stronger. In that, there is hope. If your religion is an eschatological one, you can believe than one day evil will be finished. Until then, we must live here and do what we can to create a preview of that perfect world.