The Aryan tradition is generally better than Christianity. As you would expect, what with being at least ten times as old. However, it has a distinctly Manichean obsession with identifying some part of Reality as irredeemable. Almost like Yeshua had a real point...which was, naturally, immediately missed. The Greeks had the giants in Tartarus, the Norse had Ymir, Czechs have Czernobog, the Babylonians had Tiamat... It's very consistent, which is a bit puzzling, since it doesn't work.
The Dao is somewhat bipolar, yes. Everywhere it appears as two opposites. However, it's a mobius. They're both the Dao.
Try some candidates:
Evil in the Christian sense doesn't exist. Their examples are either nonlocal and thus nonexistent, or mere examples of prudence. E.g, if hell exists, then getting condemned to hell is unwise. You're not being "selfless," you're being transcendentally selfish. Being actually selfless is both stupid and impossible.
Disorder can't be bad. Total order is death and worse than death. Everything becomes frozen solid, incapable of moving. Hint: every physical particle exists by vibrating. Absolute zero isn't merely stillness, it is nonexistence. The so-called zero-point energy is the fact that to get a particle to go completely still you have to take its particle-ness away. Some motion simply isn't optional.
Clearly if Creation is the holiest object, then Destruction must be the unholy? Excessive creation is destruction. The mobius strikes again.
Devils exist too. In this hypothetical, devils are the avatars of destruction. But destroying a devil must be bad, because destruction is bad. Which means devils are good. Which means destruction is good. Which means destroying a devil is good, which means...
Sol is hot. And that's good. Clearly, we must make him hotter, until we all broil, until the Earth evaporates, until there is no-one left to appreciate him. Or wait, no, the opposite of that moral imperative. How about never do that.
Impermanence is a blessing; your mistakes are forgiven, eventually, through destroying their consequences.
I particularly enjoy the "negative emotions" one. What happens if you do not fear? Instead of being brave, you are reckless. You take lethal risks for no reason and die, unaware that you did anything wrong. Fear is not the mind-killer, is the body-saver. Congenital analgesia is a debilitating and deadly disease, and sufferers rarely make it to 20. If they don't feel pain how do they suffer? Well, they don't exist or soon won't, so the question is moot. What happens if you do not feel anger? If you are 0/7 on wrath? You're a perennial victim. A playground for parasites. The "negative" emotions are nothing more than perfectly rational responses to negative situations. They are truth, not bad. (As long as the situation is real, anyway.) Hate? What's wrong with hating things that want to harm you? If you have a habit of loving those who wish you harm...well, then I hope and pray you both get exactly what you're asking for.
What about my own personal bugbear, lies? If nothing was concealed, it would be impossible to reveal it. Omniscience is perfection is death and worse than death. To state omniscience is good is to say the revealed religions are inherently the worship of devils, because it requires the deities to have concealed the religion in the first place. Haha, oops. No, being concealed is merely the natural way of the world, and praise be. I merely suggest that you don't try to un-reveal that which is already revealed, nor to obstruct the revelation of a secret whose time has come. Even if you temporarily succeed, it is unlikely to work out for you in the long run.
What about death? I've mentioned it a few times in a negative sense. Refer back to creation/destruction. Life without the possibility of death wasn't life in the first place.
Believing in morality is false, and falsehood is a deadly sin. Believing in morality creates the very demons it tries to combat. You isolate some healthy part of yourself, and set it up as a scapegoat. You create conflict where no conflict needs to be. You try to cut it out. It is very confused, but out of necessity it fights back. "See! The dog bites when I kick it! It must have been evil all along." You try to cut it out even harder.
If you succeed, you put something where it shouldn't be. (If you don't succeed you're doubly a chump.) You have condemned the righteous, to both your sorrows. You have created a demon.
Allegorically, you introduce oxygen into an anaerobic bacterial colony. It's not that oxygen is bad per se. It's not a devil. However, it's in the wrong place.
Having both is better than missing either. God's party is more glorious. Better for everyone to keep anaerobia and oxygen separate, that we may keep them both around.
The demon, this righteous energy placed in an unrighteous situation, is going to cause the very harms you were trying to prevent, and on top of this, the price you paid to create it will pain and weaken you.
Thus, don't believe in morality. Not morality per se, at least. (Something something mores norms normative etc.) It is ironic that hallucinating new divisions ends up uniting things which are better kept separate.
Because of the above considerations, I have difficulty giving a descriptive name for what devils are. They're anti-Dao, but that name goes clunk. They oppose Existence per se. They oppose consciousness per se. They're not khaos, which is the superposition of every possibility; they worship the absence of possibility, particularly their own possibility.
Devils are pitiful creatures, not some great and terrible adversary. They are avatars of failure in and of itself.
Certainly encountering one is never safe, but then that's exactly why they have to exist. Perfect safety is...you see the pattern...worse than death. However, no matter how much suffering they inflict upon you, they are always inflicting worse suffering upon themselves. Allegorically, what if there was a child whose parents really shouldn't love them? That's a devil.
Dissonance, I suppose I could say. If we must be Manichean, then there is an inherent conflict between harmony and dissonance. The Dao inherently can't be dissonant with the Dao, by superdivine law. Existence is a great dance, and devils are the false steps and stumbling motions that simply don't fit with any part of the greater whole. They are the incarnations of unlikeability.
If they are truly irredeemable, it is precisely and only because they aren't part of Reality.
If a devil seems powerful to you, look again. Unlike all pro-Dao spirits, their only power is that granted to them by others. They have only kratia, no dunamis. You should not worship a devil unless you wish to fail, to suffer, and to never be seen again.
But, hey, if you do wish as much? You do you.
P.S. The Buddhists are a bit hard to pin down, but they have asuras. Sure they say everyone still in the cycle is doing it wrong, but look at how they say to behave toward them. Got some Satanism in there, which is pretty impressive for a dude who pre-dated Yeshua.
The Hindus themselves seem to get it. Shiva and Kali are gods of destruction, yes, but still gods.
P.P.S. I take issue with their creation-preservation-destruction trinity, though. They forgot restoration, the principle whose avatar is archangel Raphael. I too find him to be the most humbling of archangels, and understand the urge to forget.
This dual axis is creation-restoration vs. preservation-destruction. Creation and re-creation, vs. destruction and [destruction of destruction].