How is Vegetarianism morally superior to eating meat in a Buddhist context? Fact: Buddha ate meat. He died from food poisoning eating pork. Are not thousands if not millions of living being slaughtered when you harvest vegetables (worms, insects, micro-organisms etc.)? So how is vegetarianism morally superior to eating meat in a Buddhist context?
First of all, the Buddha didn't die from eating pork at least in the Theravada point of view. In fact, his last meal was sukara maddava, translated to English dug by pigs, a mushroom which still grows in India. 

Also, vegetarianism is not considered morally superior to eating meat in Theravada. The general guideline followed with regards to eating meat by both monastics and laity is,


  I say that there are three occasions in which meat may be eaten: when it is not seen, not heard, and not suspected, that the living being has been killed for sake of the bhikkhu, I say: Meat may be eaten on these three occasions.
  MN 55


On the other hand, a person can be a strict vegetarian while craving for tastier food and could be strengthening his ego considering his higher morality, both of which are not good.