Matthew Jarpe recounts a controversial statement he made at the near future panel at ReaderCon. He was roundly dismissed for stating that if we were to go to another planet and encounter a more primitive species we would treat them better than colonizers in the past treated primitive peoples.
This brings up an important question that every science fiction writer has to address. Are people getting more moral over time? Obviously this raises a question of whether there is a quality of "morality" that can somehow be measured. I would argue that the measure would be an inclination to consider the good of a larger group than a smaller. For example, it is more moral to think of the good of your friends and family than yourself, more moral to think of the good of your city than your friends and family, more moral to think of the good of all nations than just to think of your own.
Some people (especially radical libertarians and/or conventional economists) would be inclined to disagree, arguing that reasonable self-interest can sometimes produce better results than misguided altruism, but even they would have to agree that thinking of the larger group is at least a quality of morality.
So here's the pro: think of slavery. Don't get me wrong, it is still practiced all over the world, often brutally and involving innocent children. The difference is, that it was once recognized that the master/slave relationship was just a natural state, and people kept slaves openly even in the most advanced of nations. Now people have to do it in secret, and even nations that allow slavery in practice have to at least pretend to forbid it de jure. Progress? Not nearly as much as we need, but better than nothing.
Here's the con: in the twentieth century, people have come up with entirely new and previsously unimaginable ways to be horrible to each other. The Mongols might have raced into a city and killed all the men, raped the women and enslaved the children. But once they were done with that, they'd probably have just settled down and tried to rule the place. I don't think it would have occurred to them to set up an industrialized factory like Dachau to systematically eliminate an entire race. And even the most "civilized" nations are continuously working on new and sophisticated ways to kill people.
But as I commented on Matthew's blog, I'd far rather believe that there is at least some progress, however slow it is, and however frequently we backslide. The alternative is just too unpleasant.