Well...
[spoiler=Brief Philosophical Rant.]
The universe isn't just black and white. It's also red and green, blue and orange, yellow and purple, pink and...gray? You get the point. It's possible to have a dualistic conflicts without limiting oneself to two Powers. Indeed, from a literary perspective, such a perspective can be interesting, but even without such considerations having a multipoint series of dualistic conflicts is interesting. Even if the Powers of different axes don't interact, such conflicts will shape the lives of everyday individuals. There's also how a dualistic conflict should involve a polarization of not just the followers of the Powers, but also the world itself. Multiple dualistic conflicts allow a multidimensional world to exist more simply and believably.
But yeah, GM concerns.
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The GMs have already said that the Powers are nothing like Black and White, they are both more of grey. They can be as 'evil' or as 'good' as they want, the powers simply represent a specific element/theme of life but they aren't technically restricted to act as one would typically think that element/theme works. At least that me summing up what DH told me yesterday.
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That was kinda part of my point. Also, starting with "black and white" was just convenience; most people would have had no clue what I meant if I started with "The universe isn't just purple and yellow" or something.
Paradoxally, having several pairs of Powers would make the conflict more "saturated", to keep a colourful metaphor. There will be alliances, no question over that. Order and Virtue, for example. And they will emphazise their common points. They will become more white and less grey. By limiting the conflict to a single pair, you leave a very large field open. The players will fill that field with broad, grey-ish powers. And I trust Bay12 to come up with interesting and unusual depictions of Sin, Virtue, Order, Chaos, Decay and Growth.
Of course, if the Powers were roleplayed correctly, Order and Virtue would separate once their differences became obvious--Order may support execution of a criminal, Virtue would not, while Virtue would be fine with certain activities that Order would put a stop to. In addition, any two Powers so close would have their opposites be about equally close, for obvious reasons; Chaos and Sin would share a good amount of common ground. In any case, many Powers wouldn't be associated with things that ping on the "good/evil" axis, especially how Bay12 interprets them. Remember Donut?
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