I'm not sure anger necessarily leads to discontent. If you want to get mad as hell and break things, you might feel better after doing so if you've been stifling a lot of discontent up to then. I don't really pretend to know what's going on in the head of a rioter but this seems possible.
I don't mean that actions anger predisposes you toward leave you discontented, I mean that part of the physiological emotion of anger is discontentment.
One of the most important points raised by the sequences is that not all minds are like humans. In quite a few places, people have discussed minds with slight changes from human minds, which seem altogether different. However, a lot of this discussion has been related to AI, as opposed to minds created by evolution. I'm trying to think of ways that minds which evolved, and are effective enough to start a civilization, could differ from humans'.
Three Worlds Collide would seem like an excellent starting point, but isn't actually very useful. As far as I recall, the Babyeaters might have learned their baby eating habits as a result of societal pressure. The main difference in their society seemed to be the assumption that people who disagreed with you were simply mistaken: this contrasts to humans' tendency to form rival groups, and assume everyone in the rival groups is evil. The Super-Happies had self modified, and so don't provide an example of an evolved mind.
So here are my ideas so far.