Any moral philosophy can be bad if incorrectly applied. Ontology gets abused as much as the other two, more so quite frankly. I have met more people in my life whose rigid belief that lying is always unethical regardless of the circumstances (almost like a certain character in the Dresden files...) is more dangerous than most utilitarians I have met.
Anyhow. This is a fairly cut and dry case, from the perspective I was laying out. If it really is the case that the White God gaining more followers may lead to it becoming powerful enough to let the outsiders in, than ANY necessary means is justified. We dont know that what the Denarians are doing is necessary. But it could end up being the case that their approach is the only practical one. It isnt that hard to imagine circumstances that would justify extremely Machiavellian actions to prevent a literal hell on earth via the outsiders.
It is entirely possible, probable even, that the Denarians are what the seem. A bunch of evil lunatics. I just think its extremely interesting from a narrative point of view that we havent been told precisely what made the Fallen in the DV rebel. And I dont think its past Jim to do something like this. The time we have spent with Harry as the Winter Knight has made it much less clear that Mab is evil for example.
I agree that a poorly applied philosophy or ideology can be quite awful, although I'd point out that the definition of "poorly applied" is somewhat malleable in that context. Such things by nature are open to interpretation, and everyone already interprets things slightly (sometimes not so slightly) differently. Yes, Kant's position (although he developed it from earlier ideas) was that lying was intrinsically bad - but he also wasn't a pillar of moral virtue himself, so I tend to treat it with a healthy dose of scepticism. I'm not sure which character you're referring to...although if you mean Uriel I'd point out that his real objection to lying was not from mortals, but the Fallen as their lies have far larger and more dangerous impacts (and the Fallen know better).
However, I am not sure you have considered fully the implications of your theory. Your theory assumes the worst possible outcome is victory of the Outsiders and their establishment of Hell on Earth and eventually the destruction of all (or something along those lines). I disagree. The worst possible outcome is far more horrible, in my opinion, and I believe this is why the Angels of Heaven spend so much of their resources fighting the Fallen.
Hypothetically, the worst possible outcome is that in attempting and "succeeding" to save Earth (and the Universe), humanity sacrifices it's own soul to do so. By that I mean for example, let's say Dresden had to murder and/or defile all of Earth's children in order to save the world. I don't see how that would be a world worth saving after that. Extrapolate that problem to not just Dresden having to do it, but all the adults and the problem get's infinitely worse. There are scenarios and outcomes that mean the world wouldn't be worth saving, as in attempting to keep humanity alive we would lose our humanity. We wouldn't have saved anything really. We would have created a Hell on Earth all on our own. Humanity is no so special that they should survive at the expense of all else, including their own humanity. I seem to remember the Bible having some rather extreme measures when humanity got too awful for it's own good, and it's hardly the only religion with such things.
Think about how much Uriel was prepared to sacrifice for the sake of at least ONE soul, if not several. Think about how much Dresden was prepared to sacrifice so Susan wouldn't be left at the mercy of Bianca. Think about how much Dresden, and to some extent his allies, were prepared to sacrifice for Maggie. Yes, Harry had to damage himself to save Maggie, and how much it cost his allies too (particularly Molly). But the cost to Maggie would have been worse and perhaps the cost to the world with no Harry Dresden or even Ebenezar (or even others), not to mention the cost of the Red Court winning and getting stronger. Yes, Harry condemned many to terrible fates by taking on Bianca. But that war was always going to happen regardless of Harry - he was merely the catalyst but they wanted to fight and destroy the White Council regardless, it simply came down to timing. Even Uriel's choice to give his grace to Michael Carpenter may have had extended consequences elsewhere. But given the choice between allowing bad things to happen and fighting the good fight (regardless of how hopeless it might be) I think it's clear which one is worth choosing and why.
Not everything has an "any means necessary is justified" rule. That's a philosophical position, not an objective one, and perhaps one that might be a difference in view points for some people. I don't know what your position is on that so I am not saying that is how you feel, just to be clear.
As practical as the approach of the Denarians
might be (in your theory), it still wouldn't justify their actions. The nature of their actions is often intrinsically evil, especially in the Dresden Files. Jim has confirmed there is Right and Wrong. The only way you could flip it all would be to invert what appears to be the current moral standards of the series, and declare that good is bad and vice-versa, or that there are no moral actions or positions (in an objective sense). Not talking about the real world here btw. But I don't see that being likely either.
I do agree that it is extremely interesting why the Fallen chose to rebel in the Dresden Files, and I am hoping Jim will do something a bit more interesting than "Lucifer is bad" or "Lucifer is jealous of humans" etc. I think that's been done to death. Something more along the lines of the series, like humanity being dangerous to the universe as a whole and Lucifer trying to eliminate them is interesting. Or trying to become TWG because the current one isn't so great (either in Lucifer's opinion or perhaps objectively). Or my personal fav, Lucifer is all about freedom and hates the tyranny of predestination.
But it isn't Jim's style to make the Denarians good. He has often mentioned part of why he wrote the series was to portray Christians more fairly as he often saw them portrayed as hypocrites and failures or idiots etc. He wanted characters like Michael who practiced what they preached and lived up to the ideal. Making the Denarians the good guys would fly in the face of everything he is trying to do, or has been trying to do.
Which isn't at all to say the Denarians and the Fallen at large may not think they are acting evilly. Because likely some of them, perhaps many of them, believe that they are doing is the best course of action. Maybe even believe they are moral, or at least martyring themselves by allowing themselves to take the moral hit/the weight of the sin.
