"Manners and decorum differ from culture to culture, but in their highest aim they manifest the same recognition that human beings should act with dignity, elegance, and courtesy." -- Claes G. Ryn, A Common Human Ground, p. 24
Manners are excellent domain for illustrating the point I have been stressing concerning the relationship between the universal and the particular. Much of our society falls into one of two camps on this topic, each of which, in its own way, misunderstands that relationship.
On one hand, we have those who recognize the universal element in, for instance, morality. But they miss the particularity of the way their own culture embodies the universal, and misunderstand their genuine insight as meaning that what is right for one person or one culture in one time and place must be right for all people or all cultures in all times and all places. The result is an imperious rigidity and a closure to knowledge one might glean from cultures other than one's own.
On the other hand, those who perceive that, say, whether women in a particular culture bare their breasts in public or not is a somewhat arbitrary matter, often plunge off the other side of the ledge, and decide that morality is simply made up out of whole cloth, and that therefore we can invent whatever morality we please, or even do away with the whole business altogether. They acknowledge the particular, but completely miss the universality it embodies.
We see these two mistakes made concerning manners, and perhaps it is easier to recognize them as mistakes in an area of life less contentious than morality. I think most people can bring themselves to admit that there is nothing inherently more well-mannered about eating with chopsticks than there is about eating with a fork. But hopefully they can also acknowledge that both eating with chopsticks and eating with a fork are superior to plunging your face into your plate and eating like a dog. (Superior for humans! There is nothing wrong with eating that way if you are a dog.) Both forms of utensil "manifest the same recognition that human beings should act with dignity, elegance, and courtesy."
The particular way it is judged proper to eat in your culture is somewhat arbitrary. But it is not at all arbitrary that your culture has a proper way to eat! We can accept chopsticks as the equal of forks (each in their own context), without granting eating from a pig trough the same recognition.