From an essay by Nate Blakeslee in the Wall Street Journal:
What is the difference between a dog and a wolf? From a biological perspective, the answer is simple: not much. Just a few genes in two otherwise identical strands of DNA separate dogs from their ancestors. But as an ethical question, the answer is less clear. People have persecuted wolves throughout history, for as long as shepherds have had flocks to protect. At the same time, we have venerated their direct descendants, domestic dogs, to such a degree that it is taboo to kill one in most Western societies.