Since when did compion have to be justified?

You are taking it too personally. It is not the fact that you are a vegetarian but that your diet differs from the norm. If you were to say you stopped eating vegetables, you would get the same reaction. Or if you were to say you only eat nondairy or gluten free or whatever. It is your own issues that make this question offensive to you. My wife have a limited diet. It comes off as vegetarian so many ask her if she is. But the explanation for her is that she is allergic to things so it is by necessity rather than choice. She hardly feels the need to justify and is always willing to define. Now excuse me but I have some beef cooking on the Barby and it smells GOOD ! And for my wife, bar-b-que veggies.