A bit off-track here, perhaps. I consider Charon gods evil, no question there. But is it possible to discern between degrees of evil? Is Unlife more Evil than the dark gods, and if so, for what reason? I would say yes. This will take a moment.
Orhanians and practically everyone on Kulthea uses the same source of power for spells. This source is the rift made by the Lords of Orhan as they arrived, and I think it was mentioned somewhere that its power came from a more ordered reality. Unlife is of chaos. Without going to details, I assume that the power leaking from the rift to Kulthean reality is somehow irritating or ugly to Unlife, like an oil spill on sea might be for humans. But until humans and Lords of Essaence started mucking about with it, it was nothing more than an eyesore. Actually using Essaence might be annoying to Unlife, so it reaches up from the depths of chaos and tries to swat out the source of this disturbance.
For some reason, Unlife cannot manifest or exist on Kulthean reality (perhaps it simply cannot comprehend such concepts as form or shape, but the reason is not important for now), so it does the next best thing and attempts to influence the locals and turn them against each other. And while it cannot enter this reality, it can project power to its servants. This is anti-essaence, the Power of Unlife.
But even if Unlife has very active agents who keep flipping out and killing people all the time, most of the magical power in the world is still regular essaence from the rift, which is huge compared to the conduits Unlife has drilled through. This has two results.
First, when anti-essaence can be detected, it feels wrong. Everyone on Kulthea has evolved in the presence of regular Essaence, and constant exposure to it means most people don't consider it abnormal. They may not be able to use it, but they don't fear it or worry about it much. Anti-essaence is different, and people tend to be wary of different things. So, abnormal, different, unnatural.
Second, all those murdering and destroying agents of Unlife do not really give good press to anti-essaence. Most people who are proficient in wielding it are homicidal and insane, and are considered evil (by survivors, at least). People connect these two things in their minds, and think anti-essance = evil.
Dark gods mix the pot a little. I would hazard a guess, that whatever their origins are, they were locked away and unable to touch or wield regular Essaence. Perhaps they can access it in small quantities, but nowhere as much as they would like. But when Unlife started pouring its own power to Kulthea, they realized that whoever locked regular Essaence away from them did not anticipate the existence of anti-essaence. Dark gods then learn to tap into this new power source and break out of their prison, descending upon the world. Perhaps they learned the method of accessing the power from observing Unlife's power conduits, or perhaps they are merely using some ambient anti-essaence. Anyway, they use mostly anti-essaence.
The difference between Unlife and its minions and dark gods in this example is the level of control. Regular minions are puny compared to Unlife, and as it provides power, it takes them over. Dark gods are immune to this control for some reason. They use anti-essaence simply because they can, and because it is the only source of power available to them in large quantities.
Degrees of evil, then. Real anti-essaence from Unlife is ultimately controlled by it, and is driven by its will. Even when such power is channeled through a non-corrupted host, it is still stronger and more focused. Dark gods function as power converters, and while the energy they use is still unnatural, it lacks the pure malice of Unlife. Whether the dark gods know what Unlife wants, they don't care. They want the power, so they use it. And their own methods are not always very much better, so anti-essaence still gets bad press when used.
Dark gods are the diet coke of evil compared to Unlife, but they are still evil, and evil in this case is association between the type of power and the way that power is wielded.
I also agree with Mocking Bird about the soul-annihilation imbalance.
Shift changes, gotta run home and think about this some more!