Read in August 2010. Small "novella" about space-faring humanity finding its first aliens: one race that has evolved to think eating its babies is virtuous, and one that has embraced happiness and abhors suffering on any level. The point is that the humans were horrified to find the Babyeaters and were arguing about whether to exterminate them, take them over and force them to stop their ways or just to leave them to it, when the Happy aliens appeared and had the exact same experience upon seeing us.
Disturbing. Had two endings, one in which humankind agreed to the Happy aliens' compromise and became more like them, and one in which we fled blew up a populated starsystem to prevent the Happy aliens getting to the majority of us. Neither was satisfying. I hate thinking about these sorts of things.
Actually, having thought about it some more, it's really a lot simpler than it seemed. Two races meet and one feels it has a moral obligation to intervene in the affairs of the other. It's just like war-time politics in real life. Democracy is the ideal but sometimes it comes about that emergency is declared and one country interferes forcefully with another, assuming they can't be reasoned with.
3/5 (1 in the current system?)