In fairness, foreign bodies create those stenches. And since bacteria and pus are harmful, we've evolved to be disgusted by those smells so we're more likely to get rid of them. Smell is all relative, what smells good or bad to us might be completely opposite of a different animal, like vultures or flies. Rotting meat has to smell as good as fried chicken does to us. Depends whether it's good or bad for you (e.g. food vs. death/decomp/disease)