I don't think escalating it really helps matters. Some people just seem to have a weird kind of inferiority complex when they're faced with someone who's a vegetarian/vegan for ethical reasons. People tend to feel very strongly about what they eat, I suppose. I usually take it as a sign that they might feel bad about eating meat at times. It also helps to say that you feel sorry for the animals rather than that you think it's wrong to eat them. I used the latter phrasing just once - it didn't go over well.
Usually, when people find out you're vegetarian/vegan they will ask you about it. I think it's best to stay polite and friendly because I believe that's a better way to get them to think about it.