I'd like to ask what led to this decadence in the Iridescent Tones, what were the social causes? It started out as the Cult of the Returned, and a simple faith in caring for the Returned so they'd live long enough to fulfill their purpose. And I assume the Voice even sends them back without memories exactly to foster this faith and hope in people, so that mortals can be part of their salvation instead of just getting divine hand-outs. That sounds really nice. But by the time we reach the events in Warbreaker, a lot of corruption and cynicism has found its way in, no?
Yes, it has. Part of it is something that Lightsong points out. Their religion encourages the best of the Returned to give up their lives for their people, and they hit a patch where a lot of the best of them have already given up their lives. The rest have their needs and wants seen to. Beyond that, remember this is a society in which they're living in a very temperate climate where there isn't very much harsh weather at all; they're very sheltered, they have an extremely rich resource, and they have a lot of leisure time. So we're mixing leisure time with a somewhat selfish batch of Returned in control, and we're mixing that with a religion that focuses on art and beauty and that sort of thing.
I think one of the dangers this society would have to be worried about would be for this decadence to creep in as has happened at various points in various cultures around the world. The society certainly isn't irredeemable at all, but it is going through a patch of these three concepts aligning in some of the worst sorts of ways. But there are some better Returned than we focus on in the book, and there have been much better Returned in the past.