When an DM creates a setting with a Moral Problem like this, much as like when an author starts writing a story with a conflict, there is an implied promise that you'll answer it by the end.
Oh, I agree entirely, which is why I'm coming here before the fact instead of after the fact. It's why the thread is about discussing with what it means to have a particular alignement rather than piling on me for being a DM who jerked his players around.
If your Outsiders are all certain they are right yet can't all be right, why doesn't this make any of tehm uncertain? Yes, you can claim that they are simply inscrutable and it's beyond the understanding of mere mortals but that's not a very satisfying answer.
Huston, we have an organization!

I think there should be a minority group of "rebel outsiders" who aren't so sure, and are risking their very natures to question it. Certainly figures like Dante weren't big fans of that -- the Lukewarm were the first tormented in Hell....And while the reason can be inscrutable at first, I definately want to reveal The Truth by The End, and have the PC's want to be the Heroes....but part of the problem I'm coming to ENWorld to help me with is what do the Heroes look like when saving the world means allowing people to be bad, and destroying the world could mean happiness for all? What would be *satisfying* for the PC's?
A question is whether this "respects the dignity of sentient creatures" (part of being Good) or is a form of oppression (part of being Evil). If they welcomingly embrace it, one could argue that it respects their dignity but oppression is still going to be arguable.
So is Good inherently a little Chaotic (valuing Free Will, Free Choice, even if expressed in an ordered way)? And Evil is inherently a little Lawful (valuing oppression, subjugation, even if expressed purely through random acts of cruelty)?
Not that I'm not okay with that, it just seems to be an implication...
You are talking about every alignment for themselves. And given the requirements of the Good alignment (which includes altruism), I still come back to finding it difficult to imagine every alignment, never mind every Good alignment, playing Russian Roulette with the universe with absolute certainty. I can't see the Lawful alignment taking a gamble, for example, nor can I see any Good alignment being untroubled by the implications this will have on the other Good alignments or the Neutral alignments.
Well, that's part of why no creature who advocates it views it as a gamble. It is only in mortal minds (and the minds of a few rebel, lukewarm Outsiders, now) that it's considered a gamble. The outsiders and deities see it a simple as 1+1. Of course, they all kind of disagree on what 1+1 actually equals, but each side believes it's math is completely right....the effect of the material plane being the only common meeting ground and the general lack of interest for angels to talk to devils means that there's not a lot of shared understanding between them. There's not really a dialouge because neither has ever really entertained thoughts of being at all convincing to the other side. One side *knows*, with the certainty of SCIENCE, that 1+1=Good. They hear someone say 1+1=Chaos, and they just think it's wrong...but that side *knows*, with the same certainty, that their equasion is right. They don't exactly meet to discuss the terms very often (which is part of the conflict that the PC's will be resolving, playing diplomats to idealogues). The mortals can't see/haven't yet seen the equasion, and the deities are more interested in adding than in explanation.
There is another part of this that you may be missing. While it could be argued that Good does not have to necessarily suffer the existence of Evil, Good may have to suffer the existence of Neutrality so long as the Neutral beings are "innocent" of any wrongdoing warranting their death or oppression. While it can be argued that Good can smite Evil with impunity (after all, that's why Paladins get that ability), it would be difficult to argue that Good can smite Neutral with impunity, too. The alignments are not symetrical and are not meant to be, in my opinion.
How are neutral beings innocent? They lie, they cheat, they steal, they do sometimes cruel things. They are selfish and mean. They might not be as inherently corrupt as Evil, but they are on the slippery slope, so to speak. They will not always have respect for sentient life, they will not always help those in need, and sometimes they may even take advantage of their fellow being. Must Good accomodate this?
The answer could be "yes."
The answer the [Good] Outsiders believe is "No." In fact, every alignment's exemplars see things that way: they don't have to tolerate wishy-washy inbetweeners. They don't have to do it on Elysium, why should they have to do it here? To make Heaven on Earth (in the D&D sense), why should you have to tolerate the nonbelievers?
Now, the question is, is this view *accurate*. If you have to tolerate the occasional bad thing/abusive parent/unfortunate tragedy to be Good, then the Outsiders are wrong, and the Good ones will start losing their alignment and their adherence to that cosmological power of Good. They'll fall (by the end of the campaign), and they'll be the bad guys.
If you can have Good exclusive of all other alignments (like it is in Heaven, as it should be on Earth), though, then to allow for the slightest bad thing/abusive parent/wishy-washy noncommittal miser/unfortunate tragedy is to be [Not Good Enough], and the Dragons and Fey are wrong and they'll start losing their alignment and adherence to the cosmological power of Good. They'll become debased (by the end of the campaing), and they'll be the bad guys.
And if every Outsider is equally convinced that to destroy the Prime Material Plane is to be triumphant, why don't they all simply join forced together and make it happen? If you have enough certainty to put your entire stake on a single number on a roulette wheel, why not accept help from everyone and anyone who offers it?
That's not a bad idea for the building action of the campaign.

The idea is that the material plane is remote -- outsiders generally don't just pop in unless summoned or sent by a deity, and that doesn't happen every day. However, the rate is increasing (thanks to the Grand Church), and permenant portals are being opened and it's going at such a fast rate that by the time they realize it's eroding the material plane, it's already almost too late to stop the material plane from eroding. And that the Outsiders are naturally pretty intolerant of other alignments, so working together would be like putting a square peg in a round hole -- their very natures are antithetical to each other (though the Good ones can generally tolerate this difference better than the Evil ones, of course).
Two outsiders working together would then require (a) for those outsiders to meet on the Material plane, (b) for them not to kill each other on sight, (c) for them to have a long enough conversaton to understand that they actually want the same thing, and (d) for them to doubt their own surity enough to believe that the other's goals have as much a chance for success as their own.
An unlikely, but not impossible, combination of elements. To these outsiders, blending together is like a baking soda volcano. The closer they are in alignment, the smaller the volcano, but that doesn't mean it's any less of an explosion.
Cosmological Issues: Hitchhiker's Guide to KM's Universe
[sblock]
Like someone said above, [Good], [Evil], [Law], and [Chaos] are forces, energies, substances that can be manipulated and used to your advantage. They follow the particular rule that they discriminate based on your outlook of the world -- the energies are accessed to only particular mindsets, you might say. Your belief determines how well you can access these energies. Believe life should be protected, [Good] flows into you. Believe organizations are superior methods of behavior, [Law] flows into you. This results in your alignment, and also the alignment of any other creature out there, and can be discerned and manipulated with magic just as easily as any element or energy can.
Neutrality is a state of co-dominance, or non-dominance. When it is a state of co-dominance, it's kind of the natural order of things. That's why animals, plants, and mindless creatures are neutral -- they don't really have the capacity to alter their own natural flow of moral and ethical energies. That comes with sapience, but even the sapient are under no predisposition to use these energies -- they can and many do just coast along without making use of the capacity. Non-dominance is an active purging of all moral and ethical energies from you, reaching a place above and beyond such concerns. This is the ultimate goal of the Rilmani, and is also considered "neutral." Or [Neutral], if you will.
Having an alignment other than neutral opens you up to more of one type of energy or another. This is both a boon and a problem -- certain things react well with that energy and further increase your benefits from having it. Other things react badly with that energy and actively harm you by having it. Neutrals don't suffer from this, in general, eitiher being so mixed up or so devoid of these energies that the reacting agents can't react with enough. The four alignment energies are like the four elemental energies in that they oppose one another. When fire meets water or air meets earth, both are destroyed. When good meets evil or law meets chaos, both are destroyed.
Most of the time, your alignments don't do anything directly for you right now. They determine where you wind up in the afterlife, depending upon how much of which kinds of moral or ethical energy you accumulate, but your average farmer or town's guard doesn't have to deal with these energies much. Magic can manpulate these forces like it can manipulate almost any force, to heal, to harm, to detect, etc. The magic most able to manipulate these forces is divine magic, which actually uses these forces to generate other effects.
You can train yourself (gain character classes) to use these forces, too, both in magic and inherently. The Bard or Barbarian cannot suffer an influx of much [Law], because free-form inspiration is how it gains powers. They can endure a little bit (because they can be neutral), but not much. Monks, on the other hand, are actively powered by the energies of [Law], and cannot bear a dearth of them -- they only are able to tap into new powers with a mindset that focuses on acquiring [Law] energy. The Paladin is similar, but further is enforced to gain [Good] energy as well. The Paladin's Code is the ritual through which they gain the use and manipulation of these energies, and thus violating the code ruins the ability to use the energies, as does an alignment change (which means that you've become a better or equal vessel for a different moral or ethical energy).
The Cleric is an example that is not beholden to any *specific* energy, but that potentially teaches the manipulation of any of them. Through the codes that you apply on yourself, you gain the ritual power to tap into your own stream of moral/ethical energy and use it. It even opens up a pathway to the positive or negative energy plane, depending on which moral energy you accrue the most of. Of course, if all streams are of equal strength, or if you've removed them from your system, you can't use any of them, and if the energies aren't flowing through you, you can't use them.
When a cleric or paladin falls from favor, it's much like what happens when a monk ceases to be lawful, or a barbarian starts to be lawful -- the flow of energy through you has changed so much that it interferes with the pathways you develop.
So the question for this campaign becomes "Does killing a creature with a lot of your energy dilute some of that energy in you?" Can the identical points of the magnet be brought together?[/sblock]
/END.